Ring-enlarging cyclohexane annulations

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 degrees C --> rt.