Intramolecular cyclization of alkenyl alcohols: towards the synthesis of oxacycles

The presence of tetrahydropyrans, and other sized oxacycles, in natural products with interesting pharmacological properties has prompted researchers to try to develop new strategies for their selective synthesis. Moreover, these methodologies enable the introduction of structural modifications in the molecule for the synthesis of analogues with potential biological activity. An attractive atom economy process for the synthesis of these scafolds is the intramolecular hydroalkoxylation of alkenes. However, this method has several drawbacks (such as the lack of generality and the presence of multiple side reactions) which have diminished its development.

For many years our research group has been devoted to develop different strategies for the regio-and stereoselective synthesis of oxigen and nitrogen heterocycles. Herein we present our results on the effective acid catalyzed cyclization alkenyl lacohols which bear a silyl group in their structure. As we will show, the presence of the silicon group is necessary for the cyclization to take place. Moreover, the cyclization towards tetrahydropyrans occurs with high stereoselectivity.