Sulfinyl anions conjugate additions

In their route to (- )-3, Hua and his coworkers demonstrated Ae usefiilness of chiral a-sulfinyl ketimine anions as intermediates in alkaloid synthesis (Scheme 4) (43). Treatment of the anion of 28 with (S)-( - )-menthyl p-toluenesulfinate afforded a 1 1 mixture of the separable diastereomers 29 and 30, while use of (/ )-( + )-menthyl p-toluenesulfinate afforded the enantiomers ent-29 and ent-30. Conjugate addition of the anion of 30 to methyl 2-(rerr-butoxycarbonylamino)acrylate was followed by spontaneous cyclization to give the unsaturated indolizidines 31 and 32 in a ratio of 2 3. Similar treatment of the anion of ent-29 yielded 33 and 34 in the ratio 1 2. Both sets of indolizidine diastereomers were readily separated by chromatography. The synthetic routes converged when reduction of either 32 or 33 with Raney nickel gave the same 5-oxoindolizidine 35, fiom which ( - )-slaihimine... 

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