Asymmetric cyclization of N-bridged π-allylpalladium 1,5-dipoles: synthesis of 4-methylenepyrrolidines.

A novel type of π-allylpalladium 1,5-carbodipole containing an aza-linker has been developed and employed in its self-cyclization to synthesize a series of 2-carbonyl-4-methylenepyrrolidine derivatives. Under the optimized reaction conditions, a range of substrates afforded the target products in moderate to good yields (46-84%) with good enantioselectivities (up to 84% ee; up to 99% ee after recrystallization). The synthetic utility of this method was further demonstrated by a scaled-up synthesis and product transformations.