Photoisomerization of 3-cyclooctenones

Abstract

3-Cyclooctenone and its 6-oxa analog have been found to rearrange principally to 2-vinylcyclohexanone derivatives upon irradiation. Data are presented in support of the proposal that the formation of 2-vinylcyclohexanones as well as the minor products stems from an initial Norrish type I photochemical process followed by transannular rebonding or hydrogen abstraction.

Synthetic Transformation of Abietic Acid IIIa. Photoconversion of Diene Adducts

“…Direct irradiation leads from a singulet state to a 1,3 acyl shift [12,13]. Sometimes a biradical intermediate has been discussed, but also a concerted stereospeci®c mechanism has been proposed [14±17].…”

Synthetic Applications and Methodological Developments of Donor−Acceptor Cyclopropanes and Related Compounds

“…This product is proposed to arise from a Norrish type I fragmentation of cycloheptadienone 65a , followed by intramolecular radical recombination, resulting in a net 1,3-acyl migration process. [39] …”

“…Treatment of substrate 64a with the photochemical conditions shown in Scheme resulted in the isolation of the fused cyclopentenone product 65h in good yield after a prolonged reaction time. This product is proposed to arise from a Norrish type I fragmentation of cycloheptadienone 65a , followed by intramolecular radical recombination, resulting in a net 1,3‐acyl migration process …”

The chemistry of acyl radicals

“…Similarly to radical processes occurring in the photolysis of acydic carbonyl compounds, rearrangement of the -X end of the biradical 21 produces a new radical which reacts with the acyl moiety to give rise to a new cyclic carbonyl compound. This is the case for cyclic allyl ketones, in which photochemical ~-cleavage produces smaller ring analogs 146 An analogous reaction takes place when a cyclopropyl group is in a position 3 to the carbonyl group 142, due to the well-known fact that cyclopropylcarbinyl radicals undergo ring opening leading to 3" -vinylalkyl radicals Is° (Scheme 28): 2. lntramolecular hydrogen abstraction in biradieals. The second type of rearrangement involves an intramolecular hydrogen abstraction in the biradieal.…”