Tandem Rh(II)-catalyzed 1,3-acyloxy migration/intermolecular [2+2] cycloaddition of electronically deficient propargylic esters with alkenes and alkynes

Abstract

Transition metal-catalyzed 1,3-acyloxy migration of propargylic esters represents one of the most straightforward routes to access allene intermediates, which could engage in various fascinating subsequent transformations. However, this process is often limited to propargylic esters with electron-donating group due to intrinsic electronic bias and the subsequent intermolecular reactions are quite limited. Herein, we disclosed an unprecedented Rh₂(II)-catalyzed 1,3-acyloxy migration of electron-deficient propargylic esters, followed by intermolecular [2+2] cycloaddition with readily available alkenes and alkynes, a large array of valuable alkylidenecyclobutane/ene scaffolds could be obtained facilely in one pot. Mechanistic studies revealed that the allene generated from Rh₂(II)-catalyzed 1,3-acyloxy migration of propargylic carboxylates is the key intermediate. Control experiments and NMR data indicated that the formyl group at the terminus of propargylic esters is crucial and the cooperative interactions between the substrate and the carboxylate ligand possibly play a signficant role in this reaction.