Andrey A. Mikhaylov

A Planar‐Chiral Rhodium(III) Catalyst with a Sterically Demanding Cyclopentadienyl Ligand and Its Application in the Enantioselective Synthesis of Dihydroisoquinolones

The rapid development of enantioselective C-H activation reactions has created a demand for new types of catalysts. Herein, we report the synthesis of a novel planar-chiral rhodium catalyst [(C5 H2t Bu2 CH2t Bu)RhI2 ]2 in two steps from commercially available [(cod)RhCl]2 and tert-butylacetylene. Pure enantiomers of the catalyst were obtained through separation of its diastereomeric adducts with natural (S)-proline. The catalyst promoted enantioselective reactions of aryl hydroxamic acids with strained alkenes to give dihydroisoquinolones in high yields (up to 97 %) and with good stereoselectivity (up to 95 % ee).

Three-step assembly of 4-aminotetrahydropyran-2-ones from isoxazoline-2-oxides

Tetrahydropyran-2-ones with a 4-amino function connected to a tertiary carbon atom – a widely naturally occurring fragment – are constructed by a three step protocol from easily available isoxazoline 2-oxides. In the first stage, the carbon skeleton of the target product is formed upon a C,C-coupling of a silyl ketene acetal with a nitronate function, under silyl triflate catalysis. The key step of the assembly consists of the oxidative cleavage of an endocyclic N–O bond of intermediate cyclic nitroso acetals with mCPBA, accompanied with lactone ring closure, and gives rise to β-nitro-δ-lactones in 63–85% yields. The latter are reduced with amalgamated aluminium, to furnish the target scaffold.

Extension to the Silyl-Tethered Radical Cyclization: Cyclohex-2-en-1-oxy Vinyl Silanes in Stereoselective Radical Addition/Cyclization Cascades

A novel radical cascade reaction of xanthates with 1-[(vinyldimethylsilyl)oxy]cyclohex-2-enes is developed. Due to the steric and electronic differentiation of the two olefinic functions, exclusive regioselectivity and high stereoselectivity of the addition-cyclization are observed. Several methods for modification of both the silicon tether and the xanthate function are reported.