Stereoselective Formation Of Cis-Trisubstituted 1,3-Dioxanes

Herein we report stereoselective formation of 1,3-dioxanes by oxa-Michael reaction of cis-arranged delta-siloxyenones using 1,3,5-trioxane and methanesulfonic acid (MsOH). The yields were satisfactory ranging from 81% to 95% (five examples). We furthermore studied the reaction of the ester analog with the same combination of reagents and found that stereoselective formation of tetrahydropyran by Prins reaction takes place in moderate yield of 68%. This methodology would be generally employed in the synthesis of cis-arranged heterocyclic systems which are otherwise not readily accessible.