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The Lewis acid mediated addition of organocopper reagents to the trans-ester (7a) produced the anti-isomer (8a) predominantly, while addition to the cis-derivative (7b) gave the syn-isomer (9a) preferentially, and addition of organometallic compounds to the diester (7c) also afforded the syn-isomer (9b) predominantly; this change in diastereoselectivity indicates the importance of the double bond geometry in controlling the 1,2-asymrnetric induction of y-alkoxy-a$-unsaturated carbonyl compounds. ~ ~~~The diastereoselectivity of nucleophilic addition to y-alkoxya,P-unsaturated carbonyl derivatives (1) is puzzling. Some additions have been interpreted in terms of a modified Felkin-Anh model (2), which produces the anti-isomer (3) (Scheme 1).1 1H N.m.r. analyses2 and calculations3 suggest that conformer (4), which would also give (3) as the major product, would be preferred in the ground state. It has not so far been possible to determine whether (2) or (4) is the more reactive conformer. Further, in some cases the opposite diastereoselectivity is observed; the syn-isomer (6) is pro-

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