Lignans and related phenols. Part VIII. A proof of the structures of some intermediates in arylnaphthalene synthesis

Abstract

Despite a number of earlier synthetic applications of the formation of 1-aryl-3,4-dihydronaphthalenes (V and VI) by the acid-catalysed cyclisation of aroylbutyrolactones of type (II) and/or (III), the course of reaction was illdefined, yields were variable, and there was no mechanistic explanation. Degradative and spectroscopic evidence is presented which confirms the structure (III) of the precursor, and which establishes the sequence of formation and structures of the principal intermediates, the arylisochroman (VIII) and the aryldihydrobenzocycloheptene (XVI). The variable yields of these compounds are accounted for and a mechanism for the ring contraction [e.g.(VIII) to (V)] is given.