Diastereoselective Conjugate Addition of Organocuprates to 3,4-Dimethyl-5,6-dihydro-2(1<i>H</i>)-pyridinones. A Concise Synthesis of <i>trans</i>-3,4-Dimethyl-4-phenylpiperidines
[reaction: see text] Conjugate addition of aryl or alkyl cuprates to 3,4-dimethyl-5,6-dihydro-2(1H)-pyridinones led to diastereoisomerically pure 3,4,4-trisubstituted 2-piperidinones in 39-78% yields. The yields and the diastereochemistry of piperidinones depended on both the N-protecting group and the organocuprate. Reduction then deprotection of the trans-3,4-dimethyl-4-phenyl product provided the