Rh(I)/Bisoxazolinephosphine-Catalyzed Regio- and Enantioselective Allylation of Indenes

Abstract

A highly regio- and enantioselective synthesis of chiral 3-allyl-1H-indenes has been developed using a Rh(I)/bisoxazolinephosphine catalyst in combination with 4-dimethylaminopyridine (DMAP). The tridentate NPN* ligand binds tightly to Rh(I), effectively preventing catalyst deactivation by the indene products and enabling high yields with excellent stereocontrol. Mechanistic studies reveal an unconventional pathway involving initial formation of a 1,5-diene intermediate, followed by Rh/DMAP cocatalyzed 1,3-proton migration to yield the thermodynamically favored 1,4-diene products. The method exhibits broad functional group compatibility with both allylic carbonates and indene derivatives, affording the desired products in up to 98% yield, >99% ee, and >20:1 rr.