STEREOCHEMISTRY OF ELECTROPHILIC ATTACK ON THE PUTATIVE CARBANION INTERMEDIATE IN THE BASE-CATALYZED KETONIZATION OF 3,7-DIMETHYLTRICYCLO[3.3.0.03,7]OCTAN-1-OL - EVIDENCE AGAINST AN SE1 MECHANISM FOR KETONIZATION

The putative carbanion intermediate (7) in the base-catalyzed ketonization of 3,7-dimethyltricyclo[3.3.0.03,7]octan-l-ol (1) has been generated by oxidation of the epimeric hydrazines (6) in the presence of base. The hydrazines were synthesized by a five-step sequence starting from 1,5-dimethylbicyclo[3.3.0]octane-3,7-dione (3). From either epimer of 6 deuterium capture in D2O and in (CH20D)2 by the carbanion 7 is nearly stereorandom, and ketalization of the carbonyl group in 7 has little effect on this result. The nearly stereorandom eiectrophilic attack on 7 contrasts with the essentially stereospecific incorporation of deuterium in the base-catalyzed ketonization of 1 to 2a. The retention of configuration observed in the ketonization of 1 and the contrasting stereorandom deuterium capture by 7 are both most economically accommodated by an SE2 mechanism for the transformation of 1 to 2a, although an SE1 process is not totally excluded. © 1979, American Chemical Society. All rights reserved.