Highly enantioselective and cis-diastereoselective cyclopropanation of olefins catalyzed by ruthenium complexes of (iminophosphoranyl)ferrocenes

Electrosynthesis of iminophosphoranes and applications in nickel catalysis

P(v) iminophosphorane compounds are accessed via electrochemical oxidation of commercially available P(iii) phosphines, including mono-, di- and tri-dentate phosphines, as well as chiral phosphines. The reaction uses inexpensive bis(trimethylsilyl)carbodiimide as an efficient and safe aminating reagent. DFT calculations, cyclic voltammetry, and NMR studies provide insight into the reaction mechanism. The proposed mechanism reveals a special case of sequential paired electrolysis. DFT calculations of the frontier orbitals of an iminophosphorane are compared with those of the analogous phosphines and phosphine oxides. X-ray crystallographic studies of the ligands as well as a Ni-coordination complex provide structural insight for these ligands. The utility of these iminophosphoranes as ligands is demonstrated in nickel-catalyzed cross-electrophile couplings including C(sp2)-C(sp3) and C(sp2)-C(sp2) couplings, an electrochemically driven C-N cross-coupling, and a photochemical arylative C(sp3)-H functionalization. In some cases, these new ligands provide improved performance over commonly used sp2-N-based ligands (e.g. 4,4'-di-tert-butyl-2,2'-bipyridine).

Co(II)-salen catalyzed stereoselective cyclopropanation of fluorinated styrenes

Three cis-selective Co(II)-salen complexes have been developed for the asymmetric cyclopropanation of para-fluorinated styrenes with ethyl diazoacetate. Increasing the steric reach of the C₂ -symmetric ligand side chains improved the enantiomeric ratio of the reaction from 28:1 to 66:1. The methodology was exemplified by the gram-scale synthesis of a lead compound for the treatment of castration-resistant prostate cancer (CRPC), as well as a structurally related analog.

Catalytic Enantioselective Functionalization of Unactivated Terminal Alkenes

Terminal alkenes are readily available functional groups which appear in α-olefins produced by the chemical industry, and they appear in the products of many contemporary synthetic reactions. While the organic transformations that apply to alkenes are amongst the most studied reactions in all of chemical synthesis, the number of reactions that apply to nonactivated terminal alkenes in a catalytic enantioselective fashion is small in number. This Minireview highlights the cases where stereocontrol in catalytic reactions of 1-alkenes is high enough to be useful for asymmetric synthesis.

Highly stereoselective cyclopropanation of diazo Weinreb amides catalyzed by chiral Ru(ii)–Amm–Pheox complexes

The first highly stereoselective cyclopropanation of diazo Weinreb amides with olefins was accomplished using chiral Ru(ii)–Amm–Pheox complexes to give the corresponding chiral cyclopropyl Weinreb amides in high yields.