Synthesis of Tertiary Cyclobutanols through Stereoselective Ring Expansion of Oxaspiropentanes Induced by Grignard Reagents

The stereoselectivity of the ring expansion of oxaspiropentanes to cyclobutanols induced by Grignard reagents has been studied. It has been found that the reaction occurs through the intermediacy of a cyclobutanone, formed stereospecifically, whereas the attack of the Grignard reagent on the carbonyl group of the cyclobutanone is stereospecific only in the case of the oxaspiropentanes derived from aldehydes.