Theoretical investigation on phosphine-catalyzed sequential annulation of 2-arylmethylidene cyanoacetate with Morita−Baylis−Hillman (MBH) carbonate to cyclopentane and diquinane

The first theoretical investigation was provided by our DFT calculation on phosphine-catalyzed sequential an-nulation of 2-arylmethylidene cyanoacetate and MBH carbonate. MBH carbonate was initially attacked by PMe3 to generate cation intermediate and carbon dioxide. Then proton abstraction of t-butoxyl anion gives t-butanol and resonance-stabilized zwitterionic intermediate, from which the conjugate addition and subse-quent Michael addition happens with two molecules of 2-arylmethylidene cyanoacetate. Next, the deproto-nation−reprotonation proceeds before SN2’ substitution giving desired product cyclopentane. If another molecule of cation intermediate participates in Michael addition followed by isomerization, intramolecular ad-dition, deprotonation−reprotonation and intramolecular SN2 substitution, another product diquinane with two fused five-membered ring is yielded. The deprotonation−reprotonation is rate-limiting for both products. This divergent transformation enables one-pot construction of five or four consecutive stereogenic centers, three or four new C−C bonds and one or two carbocyclic rings via [1 + 2 + 2] or [1 + 2 + 2]/[3 + 2] annulation.