Synthesis and absolute configuration of chiral (C3) cyclotriveratrylene derivatives. Crystal structure of (M)-(–)-2,7,12-triethoxy-3,8,13-tris-[(R)-1-methoxycarbonylethoxy]-10,15-dihydro-5H-tribenzo[a,d,g]-cyclononene

Abstract

The absolute configuration of chiral C₃-cyclotriveratrylene derivatives has been determined unambigously as follows. First, the absolute configuration of 2-(2-ethoxy-4-hydroxymethylphenoxy)propionic acid (5b) was established as R-(+) by chemical correlations and circular dichroism measurements. Upon treatment with perchloric acid, compound (+)-(5b) leads to the title compound (–)-(3), isolated in 14% yield, m.p. 127 °C, [α]_D²⁵–16.1°(CHCl₃). The crystal and molecular structure of (–)-(3) have been determined by single crystal X-ray analysis: orthorhombic, a= 23.428, b= 22.165, c= 15.145 Å space group P2₁2₁2₁, Z= 8. The M absolute configuration has been ascribed to (–)-(3), on the basis of internal comparison with groups –CH(Me)CO₂Me whose absolute stereochemistry is derived from that of (+)-(5b). Seven chiral C₃-cyclotriveratrylene derivatives have been chemically related to (M)-(–)-(3). The absolute configurations so established are identical with those deduced independently from an exciton analysis of circular dichroism spectra.