Photodimerization allenes

Carbene 132 is implicated in the photolysis of 1 since the observed289 photodimerization to 9,10-dihydrophenanthrene and -anthracene is best explained by head-to-head and head-to-tail coupling of this species. Moreover, the fact that allene 134 is isolated289,290 as the major product from irradiation of diesters 31 (equation 35) is fully consistent with a photo-Wolff rearrangement of the carbene. The minor product here involves cyclization... 

Photodimerizations are observed not only for olefins, but also for aromatic compounds, allenes, and acetylenes. The photodimerization of anthracene. 

Slobodin reported the photodimerization reaction of allene. Irradiation of 1,1-dimethylallene 49 affords dimers 63 and 64. The ring-opening reaction of cyclic bisallene 65 was reported by Kaupp to yield butatriene 66 on irradiation in a low-temperature matrix,and the reverse reaction from butatriene 67 to cyclic bisallene 68 in the solid state was also reported by Berkovitch-YeUin and co-workers. The photochemical racemization of optically active penta-2,3-diene 69 in hexane was reported by Rodriguez and Morrison. Kuhn and Schulz reported the photochemical ds,trans-isomerization reaction between cis-butatriene 70 and trans-butatriene 71 and also reported a 39.5% 60.5% cis-trans ratio at equilibrium upon irradiation at 313 nm. ... 

---