15-[(Z)-Phenylmethylidene]-7,14-dioxadispiro[5.1.5.2]pentadecanes: stereoselective one-pot assembly from cyclohexanones and phenylacetylene in a KOH/DMSO suspension

Cyclohexanones react with phenylacetylene in a KOH/DMSO suspension (80 °C, 1 h) to give unexpectedly phenylmethylidene dispirocyclic ketals, 15-[(Z)-phenylmethylidene]-7,14-dioxadispiro[5.1.5.2]pentadecanes, in 16-22% yields (along with the anticipated β,γ- and α,β-ethylenic ketones).