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 : I-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 N M R coupling constants. Tetrachloro-o-benzoquinone was added similarly to methoxyallene. This addition could also be performed thermally.