α- and α'-lithiation-electrophile trapping of N-thiopivaloyl and N-tert-butoxythiocarbonyl α-substituted azetidines: rationalization of the regiodivergence using NMR and computatio... by Jackson, KE, Mortimer, CL, Odell, B, McKenna, JM, Claridge, TDW, Paton, RS, Hodgson, DM