SYNTHESIS, X-RAY STRUCTURAL-ANALYSIS, AND CONFORMATIONAL STUDY OF ANTI-[3.3]METACYCLOPHANE QUINHYDRONE DIMETHYL ETHER

Synthesis and X-ray structural analysis of anti-[3.3]metacyclophane-2, 11-dione quinhydrone dimethyl ether (3) are described. The formation o f anti-3 starting from syn-9 may be ascribed to the syn-->anti isomeri zation of the syn-quinhydrone 17 according to a benzoquinone ring inve rsion process. This is in contrast to a reverse anti-->syn isomerizati on (4-->5a) of anti-[3.3]metacyclophane quinhydrone dimethyl ether 4. Results of a conformational analysis of the parent [3.3]metacyclophane s (1 and 2) and the calculated relative stability of syn and anti isom ers (3, 17 and 4, 5a) suggest that the major driving force of these sy n-anti isomerizations originates from the relative thermodynamical sta bility of the syn and anti isomers rather than from the donor-acceptor interaction between the rings. The anti geometry of 3 was confirmed b y an X-ray structural analysis.