Synthesis of substituted dibenzophospholes. Part 5. Synthesis of intermediates for 4-and 6-aryl substituents

Abstract

6-lodo-5-methoxy-8-methyl-1,2,3,4-tetrahydro-1,4-ethanonaphthalene was prepared from the Diels–Alder adduct of benzoquinone and cyclohexadiene. Diels–Alder condensation of 2-acetamidobenzoquinone and 2-iodobenzoquinone (convenient, new syntheses of both quinones are described) with 2-methylcyclohexa-1,3-diene led to mixtures of adducts; the major adduct from the iodoquinone was isolated and found by X-ray analysis to have the methyl and iodo substituents at the 2- and 7-positions, respectively, of the 1,4-ethanonaphthalene skeleton. Addition of 2-acetamidobenzoquinone to mentha-2,6,8(9)-triene derived from (–)-carvone gave two regioisomers (structures determined by n.m.r. spectroscopy). In a smooth 4-step synthesis from 6,6-dimethylfulvene and benzoquinone, 6-iodo-9-syn-isopropyl-5,8-dimethoxy-1,2,3,4-tetrahydro-1,4-methanonaphthalene was prepared and its structure confirmed by X-ray analysis.