Flavan derivatives. XVI. Acid-catalysed reactions of secondary benzyl alcohols and 1-tetralols in methanol

Abstract

Under solvolytic conditions I-phenylpropan-1-01 and its p-methyl and p-methoxy derivatives gave 1 -arylprop- 1 -enes. 1 -(3,4-Dimethoxypheny1)propan- 1-01 behaved similarly, but in addition gave the known propene dimer di-isohomogenol (di-isoeugenol dimethyl ether). Ring-proton coupling constants (J 7.3 and 9.2 CIS) appear consistent with a staggered trans-trans-configuration for this dimer,$ in agreement with earlier interpretations of chemical evidence. 1-(2,4,6-Trimethoxy- pheny1)propan-1-01 proved very reactive and gave the symmetrical dibenzyl ether under very mild acid catalysis, but with higher acid concentration it gave the prop-1-ene accompanied by a 1,l-diarylpropane formed by electrophilic displace- ment of the propan-1-01 side-chain. Tetralin-1-01 and cis- and trans-tetralin-1,2-diols, which lack activating aromatic substituents, were stable towards methanolic acetic acid (3%) or hydrogen chloride (3%). 6-Methoxytetralin-1-01, however, gave 1,6-dimethoxytetralin with methanolic 0.001% acetic acid, but with higher tetra101 concentration it gave the symmetrical bis-tetralyl ether. 6-Methoxytetralin-1-01 gave 3,4-dihydro-6-methoxynaphthalene and its known dimer when heated with methanolic hydrogen chloride (1%). Nuclear magnetic resonance showed that the tetralins are conformationally mobile, and the spectra were consistent with rapid interconversion of two half-chair conformations. 3-Phenyltetralin-1-01 (tetralin analogue of flavan-3-01) was obtained in the l,3-cis-form and existed in the confor- mationally stable half-chair form with both substituents equatorial. Spin-spin coupling constants of cis- and trans-carbonates of tetralin-1,2-diols are close to values recorded for their flavandiol analogues.