Regio- and stereoselective ring openings of unsymmetrical oxatricyclo adducts

Abstract

SN2′ ring-opening reactions of a number of substituted 11-oxatricyclo[6.2.1.01,6]undec-9-en-5-ones prepared via the intramolecular Diels–Alder reaction employing a furan diene (IMDAF) are reported. Primary, secondary, and tertiary organolithium reagents were capable of effecting the ring-opening reaction, while methyllithium required activation before any ring opening was observed. Hydride reagents, organocuprates, and Grignard reagents were generally ineffective. The ring-opening reaction was highly regio- and stereoselective for attack at C9syn to the bridging oxygen atom provided that C8 was not substituted. A highly stereoselective nucleophilic addition to the carbonyl group anti to the bridging oxygen was also observed. The high selectivity appears to be due to a combination of steric and electronic effects. Keywords: SN2′ reactions, oxatricyclo adducts, Diels–Alder reaction, ring opening.