Photochemical cycloaddition of o‐quinones to allenes; 2‐alkylidene‐2,3‐dihydro‐1,4‐dioxins

Abstract
Phenanthroquinone was added photochemically to allene and nine of its methyl, methoxy and methylthio derivatives. Several 2‐alkylidene‐2,3‐dihydrophenanthro[9,10‐b]‐1,4‐dioxins were isolated; 2: 1‐adducts were sometimes found as byproducts. The directiospecificity of the addition was investigated. The stereochemistry and conformation of the adducts are discussed in relation to long‐range NMR coupling constants. Tetrachloro‐o‐benzoquinone was added similarly to methoxyallene. This addition could also be performed thermally.

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