Guanidine-Catalyzed Triple Functionalization of [gamma]-Substituted Allenoates with Aldehydes by a Four-Step Reaction Cascade

The bicyclic guanidine 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) was discovered as an efficient catalyst for the reaction of [gamma]-substituted allenoates with aromatic aldehydes. 4H-1,3-Dioxin-6-ylpropanoates with four newly formed bonds and four stereogenic centers were obtained in good yields and excellent diastereoselectivities by two consecutive Morita-Baylis-Hillman reactions, acetalization and intramolecular Michael addition. This four-step reaction cascade not only significantly expands the scope of catalytic allenoate functionalizations but also highlights the potential of TBD to act as a multifunctional Lewis base catalyst.