Photo Diels‐Alder Additions, IV. 1,4‐Photoaddition of α‐(tert‐Butylthio)acrylonitrile to Acylnaphthalenes

Photoexcited 1‐naphthaldehyde (1a), 1‐acetonaphthone (1b) and 2‐naphthaldehyde (4) add α‐(tert‐butylthio)acrylonitrile (2b) in a [4 + 2] mode with highly regio‐ and stereoselective formation of only one diastereomer of one of the two possible regioisomeric 1,4‐dihydro‐1,4‐ethanonaphthalenes. The configuration of the products is unambiguously derived from an X‐ray crystal structure analysis for adduct 3e and an NOE experiment for compound 5. The only adduct from 1a and 2b could be detected spectroscopically but decomposed upon attempted chromatographic separation of the photolysate. Adducts 3e and 5 show first‐order retro‐cleavage into the starting materials at 50°C in CDCl3 solution with half‐lifes of 4.8 d and 11 h, respectively.