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Scheme I14753 CI CI +o, 9 2 % ; the C,-re face of the enol ether to dichloroketene attack, while positioning the C,-si face so as to be sterically shielded by the adjacent phenyl group. In reality, treatment of (-)-5 with dichloroketene (3 equiv of CC13COCI, 5 equiv of Zn-Cu)I4 in ether at 20 "C produced in excellent yield the nicely crystalline cyclobutanone (-)-6a. Most pleasingly, an examination of the crude product by 'H NMR (300 MHz) indicated that a minimum level of induction of 9 5 3 had been achieved in this cycloaddition rea~tion.'~ A single recrystallization of this material (pentane, -30 "C) efficiently provided pure (-)-6a.''Ring expansion of cyclobutanone (-)-6a with excess diazomethane in 97:3 ether-methanol at room temperature proceeded, as expected,* highly regioselectively to generate the desired dichlorocyclopentanone, which on exposure to 3 equiv of chromous perchlorate in aqueous acetoneI6 at 0 "C then cleanly furnished

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