DIFFERENTIATION BETWEEN CARBONYLS AND ACETALS IN 1,3-DITHIANE AND 1,3-DITHIOLANE SYNTHESIS CATALYZED BY ORGANOTIN TRIFLATES

Carbonyls and acetals are converted to 1,3-dithianes and -dithiolanes upon treatment with 2-stanna-1,3-dithianes and -dithiolanes under catalysis by organotin triflates. In these competition reactions, various types of carbonyls and acetals are differentiated. Aldehydes react preferentially over ketones, but the preference is completely reversed in the competition reactions between the corresponding acetals and ketals. The reactivity of aliphatic aldehydes is greater than that of the acetals of aliphatic aldehydes and ketones. Conversely, an aromatic acetal is more reactive than its parent aldehyde. In the competition between aromatic and aliphatic aldehydes, the reaction of the latter predominates. However, aromatic acetals react preferentially over aliphatic acetals. Ketones of different types are also differentiated. No such discrimination can be achieved by conventional methods. Organotin triflates are capable of detecting subtle differences in the reactivity of carbonyls and acetals. Such unique differentiation can be explained in terms of the dependence of the reaction path on the substrate: the reactions of carbonyls are initiated by coordination to tin, whereas the reactions of acetals proceed via oxocarbenium ion intermediates.