Catalytic, Enantioselective Cyclopropanation of Allylic Alcohols

Abstract

In mechanistic investigations, spectroscopic examinations and reaction surveys of substrate, reagent, and promoter were combined with solid-state evidence concerning the active form of the catalytically operative species to rationalize many of the observed features and trends of this system. Features illustrated to be critical for the best levels of stereocontrol were (1) formation of the ethylzinc alkoxide, (2) use of the Furukawa-Wittig reagent iodomethylzinc iodide, and (3) pretreatment of bis-sulfonamides such with diethylzinc. The single crystal, X-ray structure of a promoter-zinc compound revealed the likely mode of action of this species and verified its behavior as a divalent Lewis acid. A transition state rationale combining all of these features has been conceived and investigations to support this model have been conducted.