C(6)-Alkylation of 3-Hydroxypiperidine via Reductive and Homolytic Cleavage of N,S-Acetals

N-Carboxymethyl 3-hydroxypiperidine (6) undergoes substitution at C(6) via reductive cleavage of N,S-acetal 8a with lithium naphthalenide (LN) and trapping of the resulting carbanionic intermediate 9 with different electrophiles to give adducts 10. N,S-Acetal 8a also undergoes C-S homolysis and trapping of the resulting radical provides an alternative entry to 2-substituted-5-­hydroxypiperidines.