Diastereoselective and regiodivergent oxa-[3 + 2] cycloaddition of Achmatowicz products and cyclic 1,3-dicarbonyl compounds

Development of two new protocols for oxa-[3 + 2] cycloaddition reactions of Achmatowicz products with 1,3-dicarbonyl compounds for rapid and highly efficient assembly of polycyclic furopyranones is described. Plausible mechanisms were proposed to involve either Pd-catalyzed Tsuji–Trost allylation and concomitant oxa-Michael cyclization or quinine-promoted cascade Michael addition and SN2-type cycloacetalization.