Steric effects of methoxy-groups in 2,2′-bridged biphenyls. Part II

Abstract

Three o,o′-dimethoxy-bridged biphenyls, 5,7-dihydro-1,11-dimethoxydibenz[c,e]oxepin, 6,7-dihydro-1,11-dimethoxy-6,6-dimethyl-5H-dibenz[c,e]azepinium bromide (and iodide), and diethyl 6,7-dihydro-1,11-dimethoxy-5H-dibenzo[a,c]cycloheptene-6,6-dicarboxylate, have been prepared, each in both enantiomeric forms, starting from (+)- and (–)-6,6′-dimethoxydiphenic acid. Their optical stabilities have been determined and the anomalously large steric effect of the o-methoxy-groups is discussed. Their o.r.d. spectra have been measured and assignment of absolute configuration has been made; the great variation of the specific rotation of the dibenzocycloheptene with solvent (on the sodium D line) is seen as the effect of solvent on a Cotton effect situated below 220 nm.