AgOTf-catalyzed cascade annulation of 5-hexyn-1-ols and aldehydes: enabling the diastereoselective synthesis of [6,6,6]-trioxa-fused ketals and hexahydro-2<i>H</i>-chromenes

We report the unprecedented diastereoselective synthesis of novel [6,6,6]-trioxa-fused ketals <i>via</i> AgOTf-catalyzed cascade annulation of 5-hexyn-1-ols (with primary or secondary hydroxyl groups) and aldehydes through a [2+2+1+1] pathway. In contrast, 5-hexyn-1-ols with tertiary hydroxyl groups yield hexahydro-2<i>H</i>-chromenes <i>via</i> a [3+1+1+1] pathway.