Stereoselective formal [3 + 3] annulation of 3-alkylidene-2-oxindoles with β,γ-unsaturated α-keto esters.

Abstract

1,4-Diazabicyclo[2.2.2]octane (DABCO)-catalyzed [3 + 3] cycloaddition reaction of 3-alkylidene-2-oxindole and β,γ-unsaturated α-keto esters under mild reaction conditions afforded the spirocyclohexene-oxindole with excellent diastereoselectivity. The [3 + 3] annulation is found to proceed through a vinylogous Michael-aldol cascade reaction and it allows rapid access to a diverse set of highly functionalized spirocyclohexene-oxindoles. Also, a bioactivity study of the compounds on mammalian sarcoma cells has reflected cell growth inhibitory/anti-cancer properties.