ISOLABLE STEREOISOMERIC METHYLENEDIHYDROANTHRACENES - CONFORMATIONALLY ISOMERIC 9-(DICHLOROM99ETHYLENE)-10-ETHYL-10-METHYL-1,8-DICHLORO-9,10-DIHYDROANTHRACENES

Two stereoisomeric 9-(dichloromethylene)-10-ethyl-10-methyl-1,8-dichloro-9,10-dihydroanthracenes (I) have been prepared and separated and found to be stable at room temperature owing to slow boat-boat inversion of the center ring. The isomers are interconverted at temperatures above 150°. The rates of interconversion (to an equilibrium mixture containing 12% e-ethyl I) of the two isomers in sym-tetrachloroethane have been found to be first order and with k1 + k-1 = 1.5 × 10-5 sec-1 at 157°, Ea = 42.8 ± 0.6 kcal/mol, and ΔS≠ = 18 ±8 eu. 9-(Bromomethylene)-10-ethyl-10-methyl-1,8-dichloro-9,10-dihydroanthracene (V) was prepared and preliminary work suggests that it can also be separated into e-ethyl and o-ethyl isomers. Syntheses and characterizazation are described for the three compounds 9-methylene-10,10-dimethyl-1,8-dichloro-9,10-dihydroanthracene (II), 9-(dichloromethylene)-10,10-dimethyl-9,10-dihydroanthracene (III), and 9-(bromomethylene)-10,10-dimethyl-1,8-dichloro-9,10-dihydroanthracene (IV), whose nmr temperature dependence has recently beenreported.3. © 1969, American Chemical Society. All rights reserved.