Search

Simple conditions using AlCl3 for the regioselective intermolecular mono- or bis-hydroalkoxylation of allenamides are presented. The reactions showed good functional group tolerance and an initial mechanistic analysis is presented.

Regioselective intermolecular mono- or bis-hydroalkoxylation of allenamides with alcohols using simple aluminum-catalyzed reaction conditions is reported. When the reaction was carried out with 1.1 equivalents of alcohol at 50 °C, N,O-acetals were generated by 1,2-addition of an alcohol. An increase in temperature to 80 °C leads to γ-substituted ethers by an intermolecular isomerization process. Treatment with an excess of alcohol (3 equiv.) at 50 °C gave 1,3-bis(alkoxy)propanamines. The reactions exhibited good functional group tolerance and efficiency, affording the products in moderate to good yields.

The reactivity of benzyl hypervalent iodine intermediates was explored in congruence with the reductive iodonio-Claisen rearrangement (RICR) to show that there may be an underlying mechanism which expands the reasoning behind the previously known C–C bond-forming reaction. By rationalizing the hypervalent iodine’s metal-like properties it was concluded that a transmetallation mechanism could be occurring with metalloid groups such as silicon and boron. Hypervalent iodine reagents such as Zefirov’s reagent, cyclic iodonium reagents, iodosobenzene/BF3, and PhI(OAc)2/BF3 or triflate-based activators were tested. A desirable facet of the reported reaction is that iodine(I) is incorporated into the product thus providing greater atom economy and a valuable functional group handle for further transformations. The altering of the RICR’s ortho-selectivity to form para-selective products with benzyl hypervalent iodine intermediates suggests a mechanism that involves hypervalent iodine-guided electrophilic substitution (HIGES).

Phenylcyanocarbene was generated by the reaction of azide with a hypervalent iodonium alkynyl triflate and reacted in situ with 21 different carbocyclic and heterocyclic aromatic compounds. These reactions led to more complex products that frequently underwent subsequent rearrangements. The reactivity was further explored in a mechanistic study to ascertain the chemoselectivity and stereospecificity.

Dienoic acids and pentadienyl alcohols are coupled in a decarboxylative and dehydrative manner at ambient temperature using Pd(0) catalysis to generate 1,3,6,8-tetraenes. Contrary to related decarboxylative coupling reactions, an anion-stabilizing group is not required adjacent to the carboxyl group. Of mechanistic importance, it appears that both the diene of the acid and the diene of the alcohol are required for this reaction. To further understand this reaction, substitutions at every unique position of both coupling partners was examined and two potential mechanisms are presented.

Advances in hypervalent iodine chemistry have put the field on the precipice of a second golden age; the first being pioneered in the 1990s. During that period, C–C bond forming reactions would be published but rarely with the intended goal of developing a C–C bond forming methodology. More recently, the development of hypervalent iodine-guided electrophilic substitution, arylations using hypervalent iodine, and photoredox reactions with hypervalent iodine have shown great progress in the area of C–C bond formation.

A novel family of nonadentate ligands based on the (5,6-diphenyl-1,2,4-triazin-3-yl)-picolinamide donor moiety has been synthesized from simple starting materials in high yield and purity. This group of ligands is an addition to the neutral nonadentate group but the first to incorporate 1,2,4-triazine. Their ability to extract a select group of lanthanides from acidic aqueous solution has been correlated to their ability to meet the ideal trigonal tricapped prismatic geometry that is seen by lanthanides and actinides in aqueous solution. The rate of metallation was determined using UV/VIS spectroscopy with pseudo first order conditions and showed similar behaviour to literature examples. Theoretical calculations were used to probe the bonding structure with lanthanides and actinides to predict the potential Ln/An segregating ability of the new ligands.

We recently reported two unexplored reactivities of alkynes and azides. The first method reacts nucleophilic alkynes and electrophilic azides to synthesize sulfonyl-substituted 1,5-disubstituted 1,2,3-triazoles. The second method reacts electrophilic alkynes with nucleophilic azides to form alkynyl azides that immediately extrude dinitrogen to form cyanocarbenes which were trapped by O–H insertion, sulfoxide complexation, and cyclopropanation. The design and discovery of these reactions, along with key observations, is discussed herein.

Tetrakis(η3-phenylpropargyl)zirconium (3) was synthesized from ZrCl4 and (phenylpropargyl)magnesium bromide. The crystallographically determined structure of 3 exhibits D2d symmetry, consistent with the 1H and 13C NMR spectra. The electronic structure of 3 was analyzed using DFT calculations, and a HOMO−LUMO gap of 5.3 eV was calculated. The η3 coordination of the propargyl ligands and steric hindrance around the Zr center prevent the coordination of additional ligands, resulting in a homoleptic complex.

All-electron numerical density functional theory calculations with scalar relativistic corrections have been utilized to examine the mechanism of the intramolecular rhodium-catalyzed hydroacylation reaction. The gas-phase results reveal a key branch point early in the reaction at the oxidative addition step wherein the two important pathways evolve through five-coordinate Rh(III) intermediates characterized by an apical acyl group and an equatorial hydride, orientations seemingly counter to trans influence arguments. These pathways account for the gross features of the experimental product distribution as well as the isotope labeling outcomes observed by previous investigators in this area. A greatly simplified approximation to modeling the reaction environment was applied that focused on redressing the coordinative unsaturation prevalent during certain steps of the catalytic process by including an explicit molecule of solvent or an additional molecule of substrate. Such an approach allowed us to explain...

The procedures described in this article involve the synthesis and isolation of hypervalent iodonium alkynyl triflates (HIATs) and their subsequent reactions with azides to form cyanocarbene intermediates. The synthesis of hypervalent iodonium alkynyl triflates can be facile, but difficulties stem from their isolation and reactivity. In particular, the necessity to use filtration under inert atmosphere at -45 °C for some HIATs requires special care and equipment. Once isolated, the compounds can be stored and used in reactions with azides to form cyanocarbene intermediates. The evidence for cyanocarbene generation is shown by visible extrusion of dinitrogen as well as the characterization of products that occur from O-H insertion, sulfoxide complexation, and cyclopropanation. A side reaction of the cyanocarbene formation is the generation of a vinylidene-carbene and the conditions to control this process are discussed. There is also potential to form a hypervalent iodonium alkenyl triflate and the means of isolation and control of its generation are provided. The O-H insertion reaction involves using a HIAT, sodium azide or tetrabutylammonium azide, and methanol as solvent/substrate. The sulfoxide complexation reaction uses a HIAT, sodium azide or tetrabutylammonium azide, and dimethyl sulfoxide as solvent. The cyclopropanations can be performed with or without the use of solvent. The azide source must be tetrabutylammonium azide and the substrate shown is styrene.

We recently reported two unexplored reactivities of alkynes and azides. The first method reacts nucleophilic alkynes and electrophilic azides to synthesize sulfonyl-substituted 1,5-disubstituted 1,2,3-triazoles. The second method reacts electrophilic alkynes with nucleophilic azides to form alkynyl azides that immediately extrude dinitrogen to form cyanocarbenes which were trapped by O–H insertion, sulfoxide complexation, and cyclopropanation. The design and discovery of these reactions, along with key observations, is discussed herein.

A step-economical synthesis of clinprost is reported that concludes with 3 different transition metal-catalyzed reactions: Pd-catalyzed decarboxylation with allylic rearrangement, Rh-catalyzed diene-ene [2+2+1] reaction, and Ru-catalyzed cross-metathesis reaction. The complexity bestowed to the molecule from these reactions converts a readily accessible ester to clinprost without using protecting groups in only 9 total steps.