Photo Diels‐Alder Additons, V¹ 1,4‐Photoadditions of α‐Morpholinoacrylonitrile to 1‐Acylnaphthalenes

Photoexcited 1‐naphthaldehyde ( 1a ), 1‐acetonaphthone ( 1b ), and 1‐naphthophenone ( 1c ) add α‐morpholinoacrylonitrile ( 2a ) in a [4 + 2] mode with exceptional regio‐ and stereoselective formation of only one diastereomer of the two possible regioisomeric 1,4‐dihydro‐1,4‐ethanonaphthalene adducts. An independently formed 1,2‐adduct 4 was detected and isolated in very low yield, 4 is thermally and photochemically (313‐nm, excitation) cleaved into the starting materials with no indication of direct interconversion into 3b . Compound 3b is stable towards 313‐nm radiation, but is efficiently isomerized to give the dihydrobenzosemibullvalene 7 upon 254‐nm excitation. – All observations point to the first excited triplet state as the starting point for the 1,4‐additions.