Photoaddition of 2-Morpholinoacrylonitrile to Substituted 1-Acetonaphthones

Substituted 1‐acetonaphthones 6b–d and 2‐morpholinoacrylonitrile (2a) undergo a photocycloaddition. The type of addition ([2 + 2] vs. [4 + 2]) is dependent on the location of additional substituents. Whereas compound 6c with a methoxy group at C‐2 gave only the [4 + 2]‐cycloadduct 11, the formation of [2 + 2]‐cycloadducts was observed with 6b, d with cyano and methoxy groups, respectively, at C‐4. In the case of the 4‐bromo derivative 6a, photosubstitution was observed. The endo or exo orientation of the morpholino group in the cycloadducts was determined by an X‐ray crystal structure analysis for 9b, as well as by NOE signal intensity difference determination experiments for 9a and 11.