Oxa-Michael-Michael Reaction of MBH Alcohol and 2-Arylidene-1,3-indanedione: Regioselective Formal [4+2] Cycloaddition towards Tetrahydrospiropyran Scaffolds

A regioselective formal [4+2] cycloaddition reaction of nitrostyrene derived MBH alcohol and 2-arylidene-1,3-indanedione resulted in functionalized tetrahydrospiropyran derivatives with excellent chemical yields (up to 93 %). The reaction tolerated various electron rich and electron deficient substituents on the aryl group of 2-arylidene-1,3-indanedione as well as MBH alcohol. The utility of MBH alcohol as an ambident substrate, which is performing the dual role of nucleophile and electrophile with 2-arylidene-1,3-indanediones was successfully demonstrated for 20 derivatives. A single isomer was obtained exclusively in all the products via cascade process which followed an oxa-Michael-Michael addition sequence using cesium carbonate as base. Control experiments were carried out to understand the mechanistic details of the reaction. These experiments prove that the reaction undergoes a stepwise pathway rather than a concerted mechanism.