Photochemistry of Alkenes. 8. Sterically Congested Alkenes

Article abstract of DOI:10.1021/ja00414a042

A study of photobehavior of the sterically congested tri- and di-tert-butylethenes 9, 21, and 25 has afforded additional insights into the excited singlet state behavior of alkenes.In pentane solution the carbene-derived products 11, 12, 24, and 32 were formed, respectively.In methanol tri-tert-butylethene (9) afforded additionally ether 14 and the rearranged alkenes 15 and 16 derived from protonation of carbene intermediate 10. 1,1-Di-tert-butyl analogue 21 afforded no detectable ether or rearranged alkene products.However, irradiation in methanol-O-d resulted in incorporation of deuterium at the vinyl positions of 21 recovered after partial conversion, apparently from deuteration-deprotonation of carbene intermediate 22.By contrast, 1,2-di-tert-butyl isomer 25 afforded no products attributable to protonation of the corresponding carbene intermediate 23 but gave ether 35b via 1,2 addition of methanol across the double bond of 25, perhaps involving protonation of the highly polarizable orthogonal ¹(?,?^*) intermediate.