title: Synthetic and quantum mechanical studies into the N-heterocyclic carbene catalyzed (4 + 2) cycloaddition.
abstract: The N-heterocyclic carbene catalyzed (4 + 2) cycloaddition between α,β-unsaturated acid fluorides and TMS dienol ethers provides cyclohexene fused β-lactone intermediates stable below -20 °C. These can be intercepted reductively or with organolithium reagents to produce diastereomerically pure cyclohexenes (>20:1 dr) with up to four contiguous stereocenters. The mechanism has been investigated using theoretical calculations and by examining secondary kinetic isotope effects. Together these studies implicate the formation of a diastereomerically pure β-lactone intermediate by a stepwise (4 + 2) cycloaddition involving Michael addition, aldol cyclization, and lactonization.
authors.affiliation: School of Chemistry, Monash University, Clayton 3800, Victoria, Australia.
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Ryan
authors.forename: Andreas
authors.initials: A
authors.lastname: Stasch
authors.forename: Michael N
authors.initials: MN
authors.lastname: Paddon-Row
authors.forename: David W
authors.initials: DW
authors.lastname: Lupton