Enantioselective Radical‐Type 1,2‐Alkoxy‐Phosphinoylation to Styrenes Catalyzed by Chiral Vanadyl Complexes

Abstract

A series of vanadyl complexes bearing 3-tbutyl-5-bromo, 3-aryl-5-bromo, 3,5-dihalo-, and benzofused N-salicylidene-tert-leucinates was examined as catalysts for 1,2-alkoxy-phosphinoylation of 4-, 3-, 3,4-, and 3,5-substituted styrene derivatives (including Me/t-Bu, Ph, OR, Cl/Br, OAc, NO 2 , C(O)Me, CO 2 Me, CN, and benzo-fused) with HP(O)Ph 2 in the presence of t-BuOOH (TBHP) in a given alcohol or cosolvent with MeOH. The best scenario involved the use of 5 mol % 3-(2,5-dimethylphenyl)-5-Br (i.e., 3-DMP-5-Br) catalyst at 0 °C in MeOH. The desired catalytic cross coupling reactions proceeded smoothly with enantioselectivities of up to 95 % ee of (R)-configuration as confirmed by X-ray crystallographic analysis of several recrystallized products. The origin of enantiocontrol and homolytic substitution of the benzylic intermediates by vanadylbound methoxide and radical type catalytic mechanism were proposed.

Asymmetric Radical-Type 1,2-Alkoxy-Sulfenylation of Benzoxazole-2-Thiols to Vinylarenes Catalyzed by Chiral Vanadyl Complexes

“…Once V iv (O) is generated, it would facilitate the decomposition of TBHP by a Haber–Weiss-type process to form the corresponding V iv (OH)­(O 2 t -Bu) adduct. , Homolytic cleavage of its O–O bond would generate V v (O)­(OH) with the release of a t -butoxy radical (Scheme B). Hydrogen atom abstraction of H-SOxzBz by the t -butoxy radical would lead to t -BuOH and the SOxzBz radical.…”

“…At the current stage, the only asymmetric version of the radical type process by common arenethiols was recently realized by Prof. Chemler and Burde using chiral Cu­(I/II)-bisoxazoline complexes in an intramolecular manner (Scheme B). , The reactions proceeded with intramolecular asymmetric alkene oxycupration, followed by trapping of the arylsulfenyl group from a given diaryl disulfide at 120 °C. In view of our recent success in asymmetric intermolecular 1,2-alkoxyphosphinoylation of vinylarenes − (Scheme C) and the pending challenge of using REW heteroarene-thiols in asymmetric 1,2-difunctionalization of alkenes, we sought to develop the first asymmetric intermolecular variant of this type (Scheme D). In addition, the resulting products may exhibit potential anti-Alzheimer , and anti-Candida activities (Scheme E) …”

Expedient Azide–Alkyne Huisgen Cycloaddition Catalyzed by a Combination of VOSO4 with Cu(0) in Aqueous Media

“…Vanadium salts have various III, IV, and V oxidation states; vanadyl catalysts of varying counteranions can be easily prepared and applied to aqueous media at ambient temperature . As part of our ongoing research on the development of oxometallic species for catalytic transformations, we sought to develop an efficient and environmentally friendly methodology for CuAAC chemistry without the use of Cu­(II) species. We describe herein our in-depth and successful study toward this aim.…”