132 THE FORMATION OF CYCLIC KETONES ring closure may be found. It is apparent that excellent yields (examples 9 and 10) were obtained when the reaction mixture was heated for only a short period or not at all. Repetition of example 4 by other investi-gators 68 gave similar results (50-55% yields of- hydrindone-1), but by operating in the cold (example 8), consistent yields of 80% were ob-tained. The superior yield reported in 11 was obtained by a procedure which seems to warrant further investigation. The reaction was con-ducted in an inverse manner in that the acid chloride was added to the mixture of aluminum chloride in petroleum ether. The condensing agent thus was always present in excess, a condition which might serve as an explanation of the success of the cych'zation, in light of the observa-tion M that the formation of undesired bimolecular ketone condensation products is inhibited by the presence of aluminum chloride in excess of one mole. The inverse Friedel-Crafts technique has been used in a few
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