Photocycloaddition of Cyclohex‐2‐enones to 2‐Alkylprop‐2‐enenitriles

The outcome of the photocycloaddition of cyclohex‐2‐enones to 2‐alkylprop‐2‐enenitriles differs basically from that of the corresponding 2‐alkylbut‐1‐en‐3‐ynes. While the latter afford mainly products resulting from 1,6‐cyclization of the intermediate triplet alkyl‐(prop‐2‐ynyl) 1,4‐biradical, the former give only cyclobutanecarbonitriles resulting from 1,4‐cyclization of the singlet alkyl‐cyanoalkyl 1,4‐biradical.