Reagent-Controlled Regiodivergent Annulations of Achmatowicz Products with Vinylogous Nucleophiles: Synthesis of Bicyclic Cyclopenta[b]pyrans and 8-Oxabicyclo[3.2.1]octane Derivatives.

Abstract

Two reagent-controlled regiodivergent annulation protocols for Achmatowicz products with vinylogous nucleophiles have been developed, which furnished a series of bicyclic cyclopenta[b]pyrans and 8-oxabicyclo[3.2.1]octane derivatives in 28-90% yields. Plausible mechanisms were proposed to involve either Pd-catalyzed Tsuji-Trost allyl-allyl coupling and concomitant Michael cyclization or quinine-promoted cascade stepwise [5 + 2] cycloaddition and intramolecular Michael cyclization.