Exploring Acetylene Chemistry: A Transition Metal-Free Route to Dienyl 6,8-Dioxabicyclo[3.2.1]octanes from Ketones and Acetylenes.

Dienyl derivatives of 6,8-dioxabicyclo[3.2.1]octanes, closely related to naturally abundant molecules, have been synthesized from 2-acetyl-3,4-dihydropyrans (readily available from ketones and acetylene in two steps), which further add to aryl(hetaryl)acetylenes in the KOBut/DMSO superbase system (105 °C, 1.5 h) to stereoselectively give the corresponding E-styryl adducts. The latter undergo ring closure (NH4Cl/H2O, acetonitrile, reflux, 8 h) to form the 6,8-dioxabicyclo[3.2.1]octane core decorated with the (1 Z,3 E)-diene substituent.