Generation and α-hydroxyalkylation of a novel 3-piperidinol N-α-carbanion intermediate

The (S)-sulfide 6 has been synthesized as a synthetic equivalent of novel 3-piperidinol N-α-carbanion B via deprotonation and lithium naphthanelide (LN)-mediated reductive lithiation. The reaction of the 3-piperidinol N-α-carbanion intermediate B with carbonyl compounds gave, besides some reduced product 2a, the desired α-hydroxyalkylation products 12—17 with excellent 2,3-diastereoselectivity. The reductive α-hydroxyalkylation with unsymmetric carbonyl compounds led to only 50:50 to 77:23 diastereoselectiv...