Heck-Type Coupling of Fused Bicyclic Vinylcyclopropanes: Synthesis of 1,2-Dihydropyridines, 2,3-Dihydro-1 <i>H</i> -azepines, 1,4-Cyclohexadienes, and 2 <i>H</i> -Pyrans

Abstract

Herein, we report a versatile approach for the endocyclic ring opening of bicyclic vinylcyclopropanes triggered by Heck arylations. The key step for this transformation is a β-C-elimination allowing the ring expansion of cyclopropanated pyrroles, piperidines, furans, as well as cyclopentadienes to grant access to the corresponding 1,2-dihydropyridines, 2H-pyrans, 2,3-dihydro-1H-azepines, and 1,4-cyclohexadienes, respectively. Additionally, gem-disubstituted cyclopropanated furans showed unexpected behavior by giving diastereoselectively asymmetrically substituted dienes. Mechanistic studies and theoretical calculations point toward a facile β-C-elimination with a concomitant shift of Pd along the cyclopropane moiety, which can successfully compete with the usual termination step of a Heck reaction via a syn-β-hydride elimination.