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 cata lysis by organotin triflates. In these competition reactions, various types of carbonyls and acetals are differentiated. Aldehydes react pre ferentially over ketones, but the preference is completely reversed in the competition reactions between the corresponding acetals and ketal s. The reactivity of aliphatic aldehydes is greater than that of the a cetals of aliphatic aldehydes and ketones. Conversely, an aromatic ace tal is more reactive than its parent aldehyde. In the competition betw een aromatic and aliphatic aldehydes, the reaction of the latter predo minates. 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 trif lates are capable of detecting subtle differences in the reactivity of carbonyls and acetals. Such unique differentiation can be explained i n terms of the dependence of the reaction path on the substrate: the r eactions of carbonyls are initiated by coordination to tin, whereas th e reactions of acetals proceed via oxocarbenium ion intermediates.