[4+2] Cycloadditions of Seven‐Membered‐Ring trans‐Alkenes: Decreasing Reactivity with Increasing Substitution of the Seven‐Membered Ring

Abstract

The reactivity of trans ‐oxasilacycloheptenes in [4+2] cycloadditions depends on the substitution pattern on the seven‐membered ring. Unhindered trans ‐alkenes undergo [4+2] cycloadditions with 1,3‐diphenylisobenzofuran faster than the most reactive trans ‐cyclooctene. Increasing the substitution of the seven‐membered ring or increasing the electron density of the trans ‐alkene decreases reactivity with 1,3‐dienes in concerted cycloaddition reactions. Although highly substituted trans ‐alkenes are unreactive in concerted cycloaddition reactions, these alkenes react rapidly in stepwise reactions with diethyl azodicarboxylate (DEAD), an electrophilic diene.