The Photodecarbonylation of α‐Aryl Aldehydes: 1‐Formyl‐1‐methyl‐indan and heterocyclic analogues

The singlet photodecarbonylation of the indanyl aldehyde 7 – a benzohomologue of laurolenal (1) and also a conformationally rigid ‘out‐of‐plane’ analogue of the α‐aryl aldehyde 4 previously studied [5] [6], – and of the heterocyclic derivatives 8–10 in degassed solutions, has been investigated. While 7 decarbonylates uniformly to the niethylindan 30 in close analogy to the examples studied previously, 8 and 9 decompose to the corresponding Δ2‐unsaturated compounds 33, 35 in addition to decarbonylation to 32, 34. The results provide an independent indication for intermediate photolytically formed radical pairs (a) in which heteroatoms facilitate radical removal of hydrogen from C(2), and thus introduce disproportionation to give unsaturated products + CH2O, competing with the otherwise exclusive alternative affording saturated products +CO.