Catalytic enantioselective synthesis of axially chiral allenes

The development of some new synthetic reactions derived from nucleophilic addition of phosphines to electron-deficient carbon-carbon triple bonds is described. These reactions show that the phosphine plays the role of a nucleophile as well as an excellent leaving group. The central problem is to generate a 1,3-dipole from alkynoates or allenoates (2,3-butadienoates) by interaction with various phosphines. This study illuminates the unusual phenomena and shows how this understanding allows control of the reaction.

Allenes with a nucleophilic functionality connected to the alpha-carbon atom have been shown to be versatile building blocks for the syn-thesis of gamma-butenolides, gamma-lactams, gamma-iminolactones, vinylic epoxides, 4-amino-2-alkenols, 2-amino-3-alkenols, 2,5-dihydrofurans, furans, vinylic cyclopropanes, and cyclopentenes, depending on the nature of the nucleophilic centers. The reaction may proceed via the carbometalation-nucleophilic attack mechanism or nucleometallation-reductive elimination. The stereochemical outcomes by these two pathways are different.