Photodimerization of Arenediynes

photocyclization - photodimerization - arenediynes

Significance

<P>Cyclic enediynes as well as terminal acyclic enediynes are well known to undergo photochemical C^¹-C⁶ cycloaromatization. The authors explored the reactivity of naphthalenyl-substituted arenediynes (1 and 2). While the methoxy-substituted derivative 2 undergoes a photo-­Bergman cyclization upon irradiation at 300 nm, 1 shows no formation of C^¹-C⁶ or C^¹-C⁵ under these conditions. Irradiation of 1 at 350 nm, however, yields a photodimerized product (4).</P>

Comment

<P>The tandem [2+2] photocyclization yields two products in a 4:1 ratio. The structure of the major product (4) was determined by X-ray crystallographic analysis. Based on NMR studies, the authors suggest that the minor product is a ­diastereomer of 4.</P>