Synthesis of oxetane-3-carboxaldehyde and methyl oxetane-3-carboxylate via homologation of oxetane-3-one

A 4-pot telescoped procedure to prepare oxetane-3-carboxaldehyde and methyl oxetane-3-carboxylate was developed using readily available starting materials. Classical homologation methods applied to oxetane-3-one proved challenging due to the sensitivity of the oxetane ring toward strongly oxidative, basic and acidic conditions. Subsequently, a mild homologation sequence was developed. The key steps involve a Tsuji hydrogenolysis of an allylic acetate, osmium-free dihydroxylation and oxidative cleavage. Although methyl oxetane-3-carboxylate is marketed by a small number of specialty chemical companies, this work represents the first published preparation of this vital building block.