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[EN]Different densely substituted L- and D-proline esters were prepared by asymmetric (3+2) cycloaddition reactions catalyzed by conveniently selected EhuPhos chiral ligands. The gamma-nitro-2-alkoxycarbonyl pyrrolidines thus obtained in either their endo or exo forms were functionalized and coupled to yield the corresponding gamma-dipeptides. The catalytic properties of these latter dimers were examined using aldol and conjugate additions as case studies. When aldol reactions were analyzed, an additive behavior in terms of stereocontrol was observed on going from the monomers to the dimers. In contrast, in the case of the conjugate additions between ketones and nitroalkenes, the monomers did not catalyze this reaction, whereas the different gamma-dipeptides promoted the formation of the corresponding Michael adducts. Therefore, in this latter case emergent catalytic properties were observed for these novel gamma-dipeptides based on unnatural proline derivatives. Under certain conditions stoichiometric amounts of ketone, acid and nitroalkene), formation of N-acyloxy-2-oxooctahydro-1H-indoles was observed. Financial support for this work was provided by the Spanish Ministerio de Ciencia e Innovación (MICINN-FEDER, Grants PID2019-104772GB-100 and RED2018-102387-T) and the Gobierno Vasco/Eusko Jaurlaritza (GV/EJ, Grant IT-1346-19). A.R.-O. thanks the Ministerio de Ciencia, Innovación y Universidades for her Ph.D. grant. M.d.G.R thanks the DIPC and UPV/EHU for her postdoctoral contract. The authors thank Dr. José I. Miranda (SGIker-UPV/EHU) for his assistance with nuclear magnetic resonance spectroscopy. The authors also thank the SGI/IZO-SGIker of the UPV/EHU and the DIPC for generous allocations of analytical and computational resources.

The vulnerability towards CO poisoning is a major drawback affecting the efficiency and long-term performance of platinum catalysts in fuel cells. In the present work, by a combination of density functional theory calculations and mass spectrometry experiments, we test and explain the promotional effect of Ge on Pt catalysts with higher resistance to deactivation via CO poisoning. A thorough exploration of the configurational space of gas-phase Ptn + and GePtn-1 + (n=5-9) clusters using global minima search techniques and the subsequent electronic structure analysis reveals that germanium doping reduces the binding strength between Pt and CO by hindering the 2π-back-donation. Importantly, the clusters remain catalytically active towards H2 dissociation. The ability of Ge to weaken the Pt-CO interaction was confirmed by mass spectrometry experiments. Ge can be a promising alloying agent to tune the selectivity and improve the durability of Pt particles, thus opening the way to novel catalytic alternatives for fuel cells.

Here we report the highly enantio- and syn-selective synthesis of β-hydroxy α-amino acids from glycine imine derivatives under Bronsted base (BB) catalysis. The key of this approach is the use of benzophenone-derived imine of glycine o-nitroanilide as a pronucleophile, where the o-nitroanilide framework provides an efficient hydrogen-bonding platform that accounts for nucleophile reactivity and diastereoselectivity.

The high tendency of α-amino aldehydes to undergo 1,2-additions and their relatively low stability under basic conditions have largely prevented their use as pronucleophiles in the realm of asymmetric catalysis, particularly for the production of quaternary α-amino aldehydes. Herein, it is demonstrated that the chemistry of α-amino aldehydes may be expanded beyond these limits by documenting the first direct α-alkylation of α-branched α-amino aldehydes with nitroolefins. The reaction produces densely functionalized products bearing up to two, quaternary and tertiary, vicinal stereocenters with high diastereo- and enantioselectivity. DFT modeling leads to the proposal that intramolecular hydrogen bonding between the NH group and the carbonyl oxygen atom in the starting α-amino aldehyde is key for reaction stereocontrol.

The development of π-extended phosphorus heterocycles has been rapidly increasing because of their unique optoelectronics properties, which are very often considered to be a consequence of special hyperconjugative interactions. However, the latter interactions have primarily been investigated within the five-membered species, phospholes, and they are often conceptually extrapolated to the rest of π-extended phosphorus heterocycles (including six-membered P-heterocycles) despite evident structural differences. Herein, we report, for the first time, a detailed investigation that sheds light on the hyperconjugative effects of a series of phosphorus heterocyclic systems by means of EDA and NBO calculations within a DFT framework. Our results lay the foundations for the future design of π-extended phosphorus heterocycles with improved optoelectronics properties.

POX and NX halogen bonds in combination with π-stacking interactions lead to the sorting of π-extended R- and S-isomers. Theoretical calculations point to a positive synergistic effect between the π-interactions and the halogen bonds to be the origin of such phenomena. As a result, enantiomeric building blocks form homoleptically connected quadrangular structures.

Here we report the highly enantio- and

The process involving a rearrangement of pyrrolidino[3,4-c]pyrrolidine to another pyrrolidino[3,4-b]pyrrolidine using sodium methoxide as base is fully studied. The effects of the substituents are analyzed during the ring-opening/ring-closing sequence. Computational studies are also performed to explain the importance of susbstituents and quaternary carbons, especially when the (3-indolyl)methyl is present in the starting material. Finally, all the samples are evaluated as potential candidates for antibacterial and antimycobacterial activities. We are grateful for support from Mersin University [Project no: MEU-2017-COL-01007-M150D and BAP-SBE AKB (SB) 2012-8 YL and BAP 2015- AP2-1342]. We gratefully acknowledge financial support from the Spanish Ministerio de Economía y Competitividad (MINECO) (projects CTQ2013-43446-P and CTQ2014-51912-REDC), the Spanish Ministerio de Economía, Industria y Competitividad, Agencia Estatal de Investigación (AEI) and Fondo Europeo de Desarrollo Regional (FEDER, EU) (projects CTQ2016-76782-P and CTQ2016-81797-REDC), the Generalitat Valenciana (PROMETEOII/2014/017), the Gobierno Vasco/Eusko Jaurlaritza (GV/EJ, grant IT673-13), and the University of Alicante. O.L. gratefully acknowledges UPV/EHU for her postdoctoral grant. O.L. and A.d.C. gratefully thank SGI/IZO-SGIker and DIPC for generous allocation of computational resources.

A new diastereo- and enantioselective three-component cyclization reaction is described. The reaction takes place between a ketone, a carboxylic acid, and a nitroalkene to yield a bicyclic octahydro-2H-indol-2-one scaffold possessing three chiral centers. This reaction involves a rearrangement of the nitro group under simple thermal conditions. A plausible mechanism is proposed for this new reaction based on DFT calculations and isotope-labeling experiments. A new concise enantioselective synthesis of the alkaloid (+)-pancracine is presented as an example of the potential of this novel organocatalytic cyclization reaction in the synthesis of natural products.

The reaction mechanism associated with the synthesis of phosphorus-based heteropolyaromatic architectures was investigated by DFT calculations at the B3LYP-D3/6-311+G(D) level of theory. The aim of this study is to provide essential information for the future development of improved polycyclic organophosphorus materials. To that end, the impact of the structure of the initial reactant and/or the intermediates structure on the mechanistic features and energetic profiles of the phosphorus cyclization process was studied. Moreover, the reactivity parameters were analyzed in detail in a conceptual DFT framework and the underlying reactivity trends were extracted. Thus, these findings provide important insights for a rational design of polycyclic phosphorus compounds.

The enantioselective formation of nitroprolinates followed by diastereoselective Michael‐type addition onto a second unit of the nitro alkene is studied. The reaction occurred in a one pot‐sequential process controlled by the chiral phosphoramidite⋅silver benzoate complex. The origin of the high diastereoselectivity is studied by DFT computational analysis where the crucial effect of the benzoic acid is justified. The employment of this strategy to the preparation of pyrazine‐2‐ones is also surveyed, as well as the preparation of diketopiperazines from enantiomerically enriched exo‐prolinates using conventional N‐acylation‐amination‐cyclization steps. We gratefully acknowledge financial support from the Spanish Ministerio de Economía y Competitividad (MINECO), Agencia Estatal de Investigación (AEI) and Fondo Europeo de Desarrollo Regional (FEDER, EU) (pro-jects CTQ2013-43446-P, CTQ2014-51912-REDC, CTQ2016-76782-P, CTQ2016-81797-REDC and CTQ2016-76155-R), the Generalitat Valenciana (PROMETEOII/2014/017), the University of Alicante.

Catalytic enantioselective 1,3-dipolar cycloaddition between imino esters and electrophilic alkenes, employing chiral metal complexes derived from copper(I) and silver(I) salts and (S)-DM- or (S)-DTBM-Segphos as ligands produces diastereodivergently exo- or endo-cycloadducts, respectively. The effect of the functional group of the dipolarophile and the fine tuning of the catalyst plays an important role in promoting reverse diastereoselectivities. The origins of experimentally observed enantioselectivity and diastereoselectivity data, as well as the origin of the observed switched endo/exo ratios, are also explained by means of density functional theory calculations. The authors gratefully acknowledge the financial support from CAPES (Brazil), the Spanish Ministerio de Ciencia, Innovación y Universidades (projects CTQ2013-43446-P, CTQ2016-81893REDT and CTQ2014-51912-REDC), the Spanish Ministerio de Economía, Industria y Competitividad, Agencia Estatal de Investigación (AEI) and Fondo Europeo de Desarrollo Regional (FEDER, EU) (projects CTQ2016-76782-P, CTQ2016-80375-P and CTQ2016-81797-REDC), the Generalitat Valenciana (PROMETEOII/2014/017), the Gobierno Vasco/Eusko Jaurlaritza (GV/EJ, Grant IT673-13), and the University of Alicante. G.S.C. acknowledges CAPES (Brazil) for the fellowship (Process CSF-PVE-S-88887.127574/2016-00). O.L. gratefully acknowledges UPV/EHU for her postdoctoral grant.

The use of alkenyl arenes as dipolarophiles in the catalytic asymmetric 1,3-dipolar cycloaddition of azomethine ylides is reported. Under appropriate reaction conditions with a CuI or AgI catalyst either the exo or the endo adduct was obtained with high stereoselectivity. This process provides efficient access to highly enantiomerically enriched 4-aryl proline derivatives. The observed results are compatible with the blockage of one prochiral face of the 1,3-dipole, as well as with the efficient transmission of electrophilicity towards the terminal carbon atom of the dipolarophile. This polarization results in a change from a concerted to a stepwise mechanism.

A donor-stabilized 1,3-disila-2,4-diazacyclobutadiene presents an exceptionally short nonbonded Si⋅⋅⋅Si distance (2.23 Å), which is as short as that of Si=Si bonds (2.15-2.23 Å). Theoretical investigations indicate that there is no bond between the two silicon atoms, and that the unusual geometry can be related to a significant coulomb repulsion between the two ring nitrogen atoms. This chemical pressure phenomenon could provide an alternative and superior way of squeezing out van der Waals space in highly strained structures, as compared to the classical physical methods.

1,3‐Dipolar cycloadditions (1,3‐DC) between imino esters (as precursors of N‐metallated azomethine ylides) and π‐deficient alkenes are promoted by cooperative asymmetric Lewis acid/Brønsted base catalysis. The components of these catalytic pairs are silver salts derived from enantiopure commercially available BINOL‐based phosphoric acids and Cinchona alkaloids. Chiral phosphoric silver(I) salts promote HOMO raising of in situ formed 1,3‐dipoles, whereas protonated cinchona alkaloids generate a LUMO lowering for the dipolarophiles resulting in a global acceleration of the 1,3‐DC. The best results were obtained with BINOL‐derived silver phosphate and hydrocinchonine. Matching between both cooperative metallo‐ and organocatalyst results in an enhanced enantiomeric excess, superior to that reached by both separate components. NOESY experiments and DFT calculations are compatible with a non‐covalent interaction (hydrogen bond) between both catalysts, which results in close contacts and mutually coupled chiral environments. We gratefully acknowledge financial support from the Spanish Ministerio de Economía y Competitividad (MINECO) (projects CTQ2013-43446-P and CTQ2014-51912-REDC) the Spanish Ministerio de Economía, Industria y Competitividad, Agencia Estatal de Investigación (AEI) and Fondo Europeo de Desarrollo Regional (FEDER, EU) (projects CTQ2016-76782-P, CTQ2016-80375-P and CTQ2016-81797-REDC), the Generalitat Valenciana (PROMETEOII/2014/017), the Gobierno Vasco/ Eusko Jaurlaritza (GV/EJ, Grant IT673-13) and the University of Alicante. This work was partially supported by a Grant-in-Aid for Scientific Research from JSPS (17H03060).

The ion-pair SN 2 reactions of model systems MnF(n-1) +CH3Cl(M(+) =Li(+), Na(+), K(+), and MgCl(+); n=0, 1) have been quantum chemically explored by using DFT at the OLYP/6-31++G(d,p) level. The purpose of this study is threefold: 1) to elucidate how the counterion M(+) modifies ion-pair SN 2 reactivity relative to the parent reaction F(-) +CH3Cl; 2) to determine how this influences stereochemical competition between the backside and frontside attacks; and 3) to examine the effect of solvation on these ion-pair SN2 pathways. Trends in reactivity are analyzed and explained by using the activation strain model (ASM) of chemical reactivity. The ASM has been extended to treat reactivity in solution. These findings contribute to a more rational design of tailor-made substitution reactions.

Experimental and computational studies on dendrimers possessing a Fe(porphyrin) catalytic core and polyether dendritic arms show that these macromolecules promote efficiently the (2+1) cycloaddition between a model alkene and diazomethane. The reaction is kinetically efficient and competitive with smaller catalysts. Lower generations of dendrimers exhibit a normal hyperbolic kinetic behaviour, whereas third- and fourth-generation dendrimers show a sigmoidal kinetic profile, compatible with cooperative effects most likely due to aggregation phenomena. This behaviour resembles that observed for Fe(porphyrin) containing biomolecules such as cytochromes and haemoglobin.

A general synthesis of highly substituted pyrrolizidines can be performed by a multicomponent 1,3-dipolar cycloaddition using proline ester hydrochlorides, aldehydes and dipolarophiles, at room temperature without catalysts or in the presence of AgOAc (5 mol %). In the case of (2S,4R)-4-hydroxyproline derivatives it is possible to obtain enantioenriched pyrrolizidines with high control of the regio- and diastereoselectivity affording the adducts 2,4-trans-2,5-trans according to an endo-approach and a S-dipole geometry of the in situ generated azomethine ylide. For proline esters a similar regioselectivity and endo-diastereoselectivity are observed when the dipole promotes an α-attack. However, when ethyl glyoxylate is used as aldehyde component the γ-attack of the S-ylide takes place preferentially giving rise the opposite regioselectivity for acrylic dipolarophiles, being crucial the role of silver acetate. In this case, the exo-adducts with a 2,3-cis-2,5-trans relative configuration are diastereoselectively obtained. In addition, computational studies have also been carried out to shed light on the origins of the diastereo- and regioselectivity observed for the described 1,3-dipolar cycloadditions. The Spanish Ministerio de Ciencia e Innovación (MICINN) (projects CTQ2010-20387, and Consolider Ingenio 2010, CSD2007-00006), the Spanish Ministerio de Economia y Competitividad (MINECO) (projects CTQ2013-43446-P and CTQ2014-51912-REDC), FEDER, the Generalitat Valenciana (PROMETEO 2009/039 and PROMETEOII/2014/017), and the University of Alicante. L. C. M. thanks Spanish Government for a fellowship.

The competence between the possible reaction pathways in the reaction of different cycloalkanes and o-benzyne has been computationally explored. Systems able to undergo complete desaturation by consecutive double hydrogen atom transfer reactions are suggested.

A novel catalytic system based on covalently modified DNA is described., A novel catalytic system based on covalently modified DNA is described. This catalyst promotes 1,3-dipolar reactions between azomethine ylides and maleimides. The catalytic system is based on the distortion of the double helix of DNA by means of the formation of Pt(ii) adducts with guanine units. This distortion, similar to that generated in the interaction of DNA with platinum chemotherapeutic drugs, generates active sites that can accommodate N-metallated azomethine ylides. The proposed reaction mechanism, based on QM(DFT)/MM calculations, is compatible with thermally allowed concerted (but asynchronous) [π4s + π2s] mechanisms leading to the exclusive formation of racemic endo-cycloadducts.

A wide range of new dipoles and catalysts have been used in 1,3-dipolar cycloadditions of N-metalated azomethine ylides onto C60 yielding a full stereodivergent synthesis of pyrrolidino[60]fullerenes with complete diastereoselectivities and very high enantioselectivities. The use of less-explored chiral α-iminoamides as starting 1,3-dipoles leads to an interesting double asymmetric induction resulting in a matching/mismatching effect depending upon the absolute configuration of the stereocenter in the starting α-iminoamide. An enantioselective process was also found in the retrocycloaddition reaction as revealed by mass spectrometry analysis on quasi-enantiomeric pyrrolidino[60]fullerenes. Theoretical DFT calculations are in very good agreement with the experimental data. On the basis of this agreement, a plausible reaction mechanism is proposed.

This Account describes our recent studies on the chemical synthesis of cyclic, densely substituted molecules by means of a hybrid approach consisting of the synergistic interaction between computational and experimental chemistry. In addition, two related total syntheses of complex molecules (±)-Scopadulin and (-)-Exiguolide are presented as case studies in which computational chemistry can be used to detect and, eventually, avoid potential failures involving key transformations of advanced intermediates. 1 Introduction 2 Computational Treatment of Molecules 3 Computational Characterization of Reactants, Reaction Intermediates, Products and Transition Structures 4 Computational-Experimental Analysis of the Stereocontrol in Thermal Pericyclic Reactions 4.1 Concerted and Stepwise [3+2] Cycloadditions 4.2 Concerted and Stepwise [8+2] Cycloadditions 5 Total Synthesis of Complex Molecules; Two Case Studies 5.1 Total Synthesis of (±)-Scopadulin 5.2 Total Synthesis of (-)-Exiguolide 6 Conclusions and Outlook. © Georg Thieme Verlag KG Stuttgart · New York.

Density functional theory and Car-Parrinello molecular dynamics simulations have been carried out for model aldol reactions involving aggregates of lithium enolates derived from acetaldehyde and acetone. Formaldehyde and acetone have been used as electrophiles. It is found that the geometries of the enolate aggregates are in general determined by the most favorable arrangements of the point charges within the respective Lin On clusters. The reactivity of the enolates follows the sequence monomer≫dimertetramer. In lithium aggregates, the initially formed aldol adducts must rearrange to form more stable structures in which the enolate and alkoxide oxygen atoms are within the respective Lin On clusters. Positive cooperative effects, similar to allosteric effects found in several proteins, are found for the successive aldol reactions in aggregates. The corresponding transition structures show in general sofa geometries.

The stereodivergent ring-opening of 2-phenyl oxazaphospholidines with alkyl lithium reagents is reported. N-H oxazaphospholidines derived from both (+)-cis-1-amino-2-indanol and (-)-norephedrine provide inversion products in a highly stereoselective process. In contrast, N-Me oxazaphospholidines yield ring-opening products with retention of configuration at the P center, as previously reported by Jugé and co-workers. As a result, from a single amino alcohol auxiliary, both enantiomers of key P-stereogenic intermediates could be synthesized. Theoretical studies of ring-opening with model oxazaphospholidines at the DFT level have elucidated the streochemical course of this process. N-H substrates react in a single step via preferential backside S(N)2@P substitution with inversion at phosphorus. N-methylated substrates react preferentially via a two-step frontside S(N)2@P, yielding a ring-opened product in which the nucleophilic methyl binds to P with retention of configuration. DFT calculations have shown that the BH3 unit is a potent directing group to which the methyl lithium reagent coordinates via Li in all the reactions studied.

The synthesis of constrained spirocycles is achieved effectively by means of 1,3-dipolar cyclodditions employing α-imino γ-lactones as azomethine ylide precursors and nitroalkenes as dipolarophiles. The complex formed by (R,R)-Me-DuPhos 18 and AgF is the most efficient bifunctional catalyst. Final spiro-nitroprolinates cycloadducts are obtained in good to moderate yields and both high diastereo- and enantioselectivities. Density functional theory (DFT) calculations supported the expected absolute configuration as well as other stereochemical parameters.

The 1,3-dipolar cycloaddition between azomethine ylides and alkenes is efficiently catalysed by [{(Sa)-Binap-Au(tfa)}2] (Binap=2,2′-bis(diphenylphosphino)-1,1′-binaphthyl; tfa=trifluoroacetyl). Maleimides, 1,2-bis(phenylsulfonyl)ethylene, chalcone and nitrostyrene were suitable dipolarophiles even when using sterically hindered 1,3-dipole precursors. The results obtained in these transformations improve the analogous ones obtained in the same reactions catalysed by [Binap–Ag(tfa)]. In addition, computational studies have also been carried out to demonstrate both the high enantioselectivity exhibited by the chiral gold(I) complex, and the non-linear effect observed in this transformation. This work has been supported by the DGES of the Spanish Ministerio de Ciencia e Innovación (MICINN) (Consolider Ingenio 2010 CSD2007-00006, FEDER-CTQ2007-62771/BQU, CTQ2007/67528, CTQ2010-20387 and by the Hispano-Brazilian project PHB2008-0037-PC), Generalitat Valenciana (PROMETEO/2009/039), the Basque government (grant IT-324-07) and by the University of Alicante.

The synthesis of the first isolable C-phosphino-Ge-aminogermyne, stabilized by a phosphine ligand, has been achieved. X-ray diffraction analysis indicates a quite long Ge-C bond whose length is between that of a single and a double bond but consistent with the theoretically predicted values for a germyne bearing π-donating substituents. The isomerization of this germyne derivative affords a new stable N-heterocyclic germylene through migration of the original phosphine ligand from germanium to the carbon center.

The synthesis of a GSK 2(nd) generation inhibitor of the hepatitis C virus, by enantioselective 1,3-dipolar cycloaddition between a leucine derived iminoester and tert-butyl acrylate, was studied. The comparison between silver(I) and gold(I) catalysts in this reaction was established by working with chiral phosphoramidites or with chiral BINAP. The best reaction conditions were used for the total synthesis of the hepatitis C virus inhibitor by a four step procedure affording this product in 99% ee and in 63% overall yield. The origin of the enantioselectivity of the chiral gold(I) catalyst was justified according to DFT calculations, the stabilizing coulombic interaction between the nitrogen atom of the thiazole moiety and one of the gold atoms being crucial. This work has been supported by the DGES of the Spanish Ministerio de Ciencia e Innovacion (MICINN) (Consolider INGENIO 2010 CSD2007-00006, FEDER-CTQ2007-62771/BQU, CTQ2007/67528, CTQ2010-20387 and by the Hispano-Brazilian project PHB2008-0037-PC), Generalitat Valenciana (PROMETEO/ 2009/039), the Basque government (Grant IT-324-07) and by the University of Alicante. M. M.-R. Also thanks DGES for a grant.

The thermal [4+3] cycloaddition reaction between allenes and tethered dienes (1,3-butadiene and furan) assisted by transition metals (Au I , Au III , Pd II , and Pt II ) was studied computationally within the density functional theory framework and compared to the analogous non-organometallic process in terms of activation barriers, synchronicity and aromaticity of the corresponding transition states. It was found that the metal-mediated cycloaddition reaction is concerted and takes place via transition structures that can be even more synchronous and more aromatic than their non-organometallic analogues. However, the processes exhibit slightly to moderately higher activation barriers than the parent cycloaddition involving the hydroxyallylic cation. The bond polarization induced by the metal moiety is clearly related to the interaction of the transition metal with the allylic π * molecular orbital, which constitutes the LUMO of the initial reactant. Finally, replacement of the 1,3-butadiene by furan caused the transformation to occur stepwise in both the non-organometallic and metal-assisted processes.

The enantioselective Taniaphos·silver fluoride-catalyzed enantioselective 1,3-dipolar cycloaddition using 2,2-dimethoxyacetaldehyde derived imino esters and maleimides is described. The employment of this complex allows the reaction in the absence of an extra base giving high yields and ee of the corresponding endo-cycloadducts. Calculations performed at B3LYP/6-31G*&LANL2DZ level of theory predicted the expected absolute stereochemistry for both BINAP and Taniaphos·silver fluoride-mediated cycloadditions, as well as the enantioselectivity and mild conditions of the reaction. Financial support was provided by the Spanish Ministerio de Ciencia e Innovación (MICINN) (projects CTQ2010-20387, and Consolider Ingenio 2010, CSD2007-00006), the Spanish Ministerio de Economía y Competitividad (MINECO) (projects CTQ2013-43446-P, and CTQ2014-51912-REDC), FEDER, the Generalitat Valenciana (PROMETEO 2009/039 and PROMETEOII/2014/017), the University of Alicante, the Gobierno Vasco/Eusko Jaurlaritza (Grant IT673-13), and the Univeristy of the Basque Country UPV/EHU (UFI11/22 QOSYC).

Experimental and computational studies on the formation of aryl azides from the corresponding diazonium salts support a stepwise mechanism via acyclic zwitterionic intermediates. The low energy barriers associated with both transition structures are compatible with very fast and efficient processes, thus making this method suitable for the chemical synthesis of radiolabelled aryl azides. Funding Agencies|RADIOMI project (EU FP7-PEOPLE-ITN-RADIOMI); Ministerio de Economia y Competitividad (MINECO) of Spain; FEDER [CTQ2013-45415-P]; University of the Basque Country (UPV/EHU) [UFI11/22 QOSYC]; Basque Government (GV/EJ) [IT-324-07]

Chiral complexes formed by privileged phosphoramidites and silver triflate or silver benzoate are excellent catalysts for the general 1,3-dipolar cycloaddition between azomethine ylides generated from alpha-amino acid-derived imino esters and nitroalkenes affording the exo-cycloadducts (4,5-trans-2,5-cis-4-nitroprolinates) with high diastereo- and enantioselectivity at room temperature.

Chiral complexes formed by privileged phosphoramidites derived from chiral binol and optically pure Davies’ amines, and copper(II) triflate, silver(I) triflate or silver(I) benzoate are excellent catalysts for the general 1,3-dipolar cycloaddition between nitroalkenes and azomethine ylides generated from α-amino acid derived imino esters. These three methods can be conducted at room temperature to afford the exo-cycloadducts (4,5-trans-2,5-cis-4-nitroprolinates) with high diastereoselectivity and high enantioselectivity. In general, the three procedures are complementary but silver catalysts are more versatile and less sensitive to sterically congested starting materials. This work has been supported by the Spanish Ministerio de Ciencia e Innovación (MICINN) (Consolider INGENIO 2010 CSD2007-00006, CTQ2010-20387) and Ministerio de Economía y Competitvidad (MINECO) (CTQ2013-43446P, CTQ2014-51912-REDC), FEDER, Generalitat Valenciana (PROMETEO/2009/039 and 2014/017), and by the University of Alicante. L.M.C. thanks the MICINN for a FPI fellowship. Financial support was also provided by the MICINN and FEDER (projects CTQ2010-16959/BQU), the University of the Basque Country (UPV/EHU, UFI11/22QOSYC) and the Basque Government (GV/EJ, grant IT-324-07).

A wide range of new dipoles and catalysts have been used in 1,3-dipolar cycloadditions of N-metalated azomethine ylides onto C60 yielding a full stereodivergent synthesis of pyrrolidino[60]fullerenes with complete diastereoselectivities and very high enantioselectivities. The use of less-explored chiral α-iminoamides as starting 1,3-dipoles leads to an interesting double asymmetric induction resulting in a matching/mismatching effect depending upon the absolute configuration of the stereocenter in the starting α-iminoamide. An enantioselective process was also found in the retrocycloaddition reaction as revealed by mass spectrometry analysis on quasi-enantiomeric pyrrolidino[60]fullerenes. Theoretical DFT calculations are in very good agreement with the experimental data. On the basis of this agreement, a plausible reaction mechanism is proposed.

3 páginas, 2 figuras, 1 tabla, 3 esquemas., The synthesis and structural characterization of a mixed-sandwich (η5-C5Me5)Rh(III) complex of the cyclometalated phosphine PMeXyl2 (Xyl = 2,6-C6H3Me2) with unusual κ4-P,C,C′,C′′ coordination (compound 1-BArf; BArf = B(3,5-C6H3(CF3)2)4) are reported. A reversible κ4 to κ2 change in the binding of the chelating phosphine in cation 1+ induced by dihydrogen and hydrosilanes triggers a highly efficient Si−H/Si−D (or Si−T) exchange applicable to a wide range of hydrosilanes. Catalysis can be carried out in an organic solvent solution or without solvent, with catalyst loadings as low as 0.001 mol %, and the catalyst may be recycled a number of times., Financial support (FEDER support) from the Spanish Ministerio de Educación (Project No. CTQ2007-62814), Consolider-Ingenio 2010 (No. CSD2007-0000), and the Junta de Andalucía (Projects Nos.FQM-119 and P09-FQM-4832) is gratefully acknowledged. J.C. thanks the Ministerio de Educación for a research grant (Ref. AP20080256), and A.C.E. thanks CONACYT (Mexico) for a research grant (Ref. No. 22934).

It is demonstrated that BINOL derived phosphoramidite is an excellent ligand for the Cu(OTf)2 catalyzed 1,3-dipolar cycloaddition of azomethine ylides and nitroalkenes.

This Account describes our recent studies on the chemical synthesis of cyclic, densely substituted molecules by means of a hybrid approach consisting of the synergistic interaction between computational and experimental chemistry. In addition, two related total syntheses of complex molecules (±)-Scopadulin and (–)-­Exiguolide are presented as case studies in which computational chemistry can be used to detect and, eventually, avoid potential failures involving key transformations of advanced intermediates. 1 Introduction 2 Computational Treatment of Molecules 3 Computational Characterization of Reactants, Reaction ­Intermediates, Products and Transition Structures 4 Computational–Experimental Analysis of the Stereocontrol in Thermal Pericyclic Reactions 4.1 Concerted and Stepwise [3+2] Cycloadditions 4.2 Concerted and Stepwise [8+2] Cycloadditions 5 Total Synthesis of Complex Molecules; Two Case Studies 5.1 Total Synthesis of (±)-Scopadulin 5.2 Total Synthesis of (–)-Exiguolide 6 Conclusions and Outlook

Chiral complexes formed by phosphoramidites such as (Sa,R,R)-9 and Cu(OTf)2 are excellent catalysts for the general 1,3-dipolar cycloaddition between azomethine ylides and nitroalkenes affording the corresponding tetrasubstituted proline esters mainly as exo-cycloadducts in high er at room temperature. The exo-cycloadducts can be obtained in enantiomerically pure form just after simple recrystallization. DFT calculations support the stereochemical results. This work has been supported by the Spanish Ministerio de Economía y Competitividad (MINECO) (Consolider INGENIO 2010 CSD2007-00006, CTQ2010-20387), FEDER, Generalitat Valenciana (PROMETEO/2009/039), and the University of Alicante. L.M.C. thanks the MINECO for an FPI fellowship.

The BINAP-gold(I) catalyst shows similar or improved activity in a series of enantioselective Diels—Alder reactions, when compared to the BINAP-silver catalyst.

The catalytic enantioselective [3+2] cycloaddition between azomethine ylides and α,β-unsaturated aldehydes catalyzed by α,α-diphenylprolinol has been studied in detail. In particular, the reaction has been extended to the use of 2-alkenylidene aminomalonates generated in situ as azomethine ylide precursors. These reactions lead to the formation of pyrrolidines containing a 5-alkenyl side chain with potential for chemical manipulation. Moreover, a detailed and concise computational study has been carried out to understand the exact nature of the mechanism of this reaction and especially the consequences derived from the incorporation of the chiral secondary amine catalyst on the reaction pathway.

In this article we present recent developments in (3+2) cycloadditions with special emphasis on 1,3-dipolar reactions involving azomethine ylides and alkenes possessing electron withdrawing groups. It is found that there is not a general mechanism for these reactions since both concerted aromatic [(π)4(s)+(π)2(s)] mechanisms and stepwise processes involving zwitterionic intermediates can be found. These computational models can be extended to analyse the role of chiral catalysts in these reactions in order to understand the nature of the catalytic cycle and the origins of chiral induction.