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The reactivity of the pyridyl-substituted aziridine with different N-, S-, and O-nucleophiles is examined in order to understand the optimal conditions allowing for a selective ring-opening. It is shown that complete or prevalent regioelectivity can be obtained by using cerium trichloride heptahydrate as a catalyst and the N-substituent can be removed by an oxidative protocol.

The organometallic allylation of 2-pyrroleimines derived from (S)-valinol and (S)-phenylglycinol ring-closing metathesis (RCM) reaction and pyrrole ring hydrogenation are used to synthesize the N-protected 8-aminoindolizidines. The auxiliary based method starting from 2-pyrrolealdehydes could also be applied to prepare all the possible stereoisomers of amino-substituted fused bicyclic compounds containing the pyrrolidine nucleus.

An aziridination procedure for 2-pyridineimines derived from [beta]-amino alcohols and [alpha]-aminoacid esters and the reactivity of the aziridine ring toward external nucleophiles is described. The findings suggest that the chemical functionality present in the nitrogen substituent could be exploited to achieve regioselective and stereoselective ring opening reactions by halide ions and an unusual rearrangement to a substituted pyrroline.

The facial solvation of (R)-2-phenyl-propionaldehyde in n-pentane and n-octane at a number of temperatures is studied using molecular dynamics simulations and is compared with experimental selectivity data for the nBuLi addition leading to syn and anti-(2R)-2-phenyl-3-heptanol, which give nonlinear eyring plots with the presence of inversion temperatures. It is found from simulations that the facial solvation changes with temperature and alkane.

New chiral perazamacrocycles containing four pyrrole rings have been synthesized by the [2 + 2] condensation of (R,R)-diaminocyclohexane and 5,5'-(alkane-2,2-diyl)bis(1H-pyrrole-2-carbaldehydes). These macrocycles, differing for the alkyl/aryl meso-substituents, were used as ligands in the copper-catalyzed Henry reactions of aromatic and aliphatic aldehydes with nitroalkanes. In the optimized experimental conditions, the condensations of nitromethane and aromatic and aliphatic aldehydes in the presence of catalytic amounts of copper diacetate and methyl-substituted macrocyclic ligand (2:1 ratio) in ethanol at room temperature provided products often with high enantiomeric excesses (up to 95% ee). The positive influence of the macrocyclic structure on the efficiency/enantioselectivity of the catalytic system was demonstrated by comparison with the outcomes of Henry reactions performed using analogous macrocyclic ligands (trianglamines) and open-chain ligands derived from (R,R)-diaminocyclohexane. [ABSTRACT FROM AUTHOR]

1-Allyl-2-pyrroleimines obtained from (S)-valinol and (S)-phenylglycinol underwent highly diastereo; selective addition of allylmagnesium chloride, used in excess amounts, to give the corresponding secondary amines with concomitant allyl to (Z)-1-propenyl isomerization of the 1-pyrrole substituent. Transformation of the 2-amino alcohol moiety to an oxazolidinone, or its cleavage and subsequent N-protection, followed by ring-closing metathesis of the two alkene groups gave the unsaturated bicyclic compound. Full hydrogenation of the alkene function and the aromatic rings afforded the indolizidine derivative as a mixture of two or three diastereomers with a ratio which was dependent on the nature of both the N-substituent and the catalyst. The two prevalent diastereomers were isolated, and their configuration was determined by X-ray crystallographic analysis. [ABSTRACT FROM AUTHOR]

This work is concerned with the rationalization and prediction of solvent and temperature effects in nucleophilic addition to α-chiral carbonyl compounds leading to facial diastereoselectivity. We study, using molecular dynamics simulations, the facial solvation of (R)-2-phenyl-propionaldehyde in n-pentane and n-octane at a number of temperatures and compare it with experimental selectivity data for the nBuLi addition leading to syn- and anti-(2R)-2-phenyl-3-heptanol, which give nonlinear Eyring plots with the presence of inversion temperatures. We have found from simulations that the facial solvation changes with temperature and alkane. Moreover, by introducing a suitable molecular chirality index we have been able to predict break temperatures (Tcl) for the two solvents within less than 20° of the inversion temperatures experimentally observed in the diastereoselective nBuLi addition. We believe this could lead to a viable approach for predicting inversion temperatures and other subtle solvent effects in a number of stereoselective reactions. [ABSTRACT FROM AUTHOR]

A practical and effective photoredox propargylation of aldehydes promoted by 10 mol % of [Cp 2 TiCl 2 ] is presented. No stoichiometric metals or scavengers are used for the process. A catalytic amount of the cheap and simply prepared organic dye 3DPAFIPN is used as the reductant for titanium. The reaction displayed a broad scope, and no traces of allenyl isomers were detected for simple propargyl bromide, whereas mixtures of propargyl and allenyl isomers were observed for substituted propargyl bromides.

We combine ambient (air) and ultrahigh vacuum (UHV) scanning tunneling microscopy (STM) and spectroscopy (STS) investigations together with density functional theory (DFT) calculations to gain a subnanometer insight into the structure and dynamic of two-dimensional (2D) surface-supported molecular networks. The planar tetraferrocene-porphyrin molecules employed in this study undergo spontaneous self-assembly via the formation of hydrogen bonded networks at the gold substrate-solution interface. To mimic liquid phase ambient deposition conditions, film formation was accomplished in UHV by electro-spraying a solution of the molecule in chloroform onto an Au(111) substrate, thereby providing access to the full spectroscopic capabilities of STM that can be hardly attained under ambient conditions. We show that molecular assembly on Au (111) is identical in films prepared under the two different conditions, and in good agreement with the theoretical predictions. However, we observe the contrast found for a given STM bias condition to be different in ambient and UHV conditions despite the similarity of the structures, and we propose possible origins of the different imaging contrast. This approach could be valuable for the thorough characterization of surface systems that involve large molecules and are prepared mainly in ambient conditions.

Hydroboration of (1R,2R)-bis[(S)-1-phenylethylamino]cyclohex-4-ene and its derivatives with several borane reagents gave diastereomeric mixtures of the 3,4-diaminocyclohexanol derivatives. Cyclization of the prevalent diastereomer with the R configuration of the newly formed stereocenter under Mitsunobu conditions, followed by reductive removal of the N-substituents, gave the optically pure endo-7-azabicyclo[2.2.1]heptane-2-amine.