Ring-Enlarging Cyclohexane Annulations

Abstract

A Prins−pinacol rearrangement is the key step in a new method for synthesizing cis -bicyclo[ n .4.0]alkanones. The alkenyl acetal rearrangement substrates 1 are assembled from cycloalkanone precursors in four steps (Table 1). Prins−pinacol rearrangement to form cis -bicyclo[ n .4.0]alkanones 3 is best accomplished by exposure of 1 to 1 equiv of TMSOTf and a proton scavenger (2,6-di- tert -butyl-4-methylpyridine) at −78 °C → rt.