Allenes in asymmetric catalysis: Asymmetric ring opening of meso-epoxides catalyzed by allene-containing phosphine oxides

(Chemical Equation Presented) Unsymmetrically substituted allenes (1,2-dienes) are inherently chiral and can be prepared in optically pure form. Nonetheless, to date the allene framework has not been incorporated into ligands for asymmetric catalysis. Since allenes project functionality differently than either tetrahedral carbon or chiral biaryls, they may create complementary chiral environments. This study demonstrates that optically active, C ₂-symmetric allene-containing bisphosphine oxides can catalyze the addition of SiCl₄ to meso-epoxides with high enantioselectivity. The epoxide opening likely involves generation of a Lewis acidic, cationic (bisphosphine oxide)SiCl₃ complex. The fact that high asymmetric induction is observed suggests that allenes may represent a new platform for the development of ligands and catalysts for asymmetric synthesis.