Photochemical Route to a Represantative 1,8-Annulated 7-Methylene-1,3,5-cyclooctatriene

Article abstract of DOI:10.1021/jo00376a034

The bifunctional 2-cyclohexanone that is produced by addition of the Grignard reagent derived from 6-chloro-2-hexyne to 3-ethoxycyclohexenone was irradiated. <2 + 2> Cycloaddition occurred to produce a highly sensitive tricyclic cyclobutene (14), which underwent ready double-bond migration in the presence of palladium(II) acetate.With the exocyclic ? bond in position, the α,β-unsaturated ketone functionality was next elaborated.Although oxidation of 15 via organoselenium methodology did give 16, the yield was only modest.A more expedient approach involved initial con version of 14 to its silyl enol ether and concurrent oxidation-olefin isomerization with Pd(II).Hydride reduction of the resulting dienone proceeded stereospecifically to deliver an allylic alcohol that underwent smooth dehydratation to give the target hydrocarbon 11 when treated with 2,4-dinitrobenzenesulfenyl chloride and triethylamine.The available evidence suggests that disrotatory ring opening within intermediate 18 occurs readily.