Pseudo-axial disposition

Enantiopure cis- and trani-2,6-dialkylpiperidines were synthesized from the same 6-alkylpiperidine-2-one. In order to relieve A strain in the intermediate iminium ion, the 6-alkyl substituent is in a pseudo-axial disposition and nucleophilic attack occurs from the axial direction to give the cis product <03JOC1919>. 

The splitting pattern and coupling constants fOT the C-2 melhine hydrogen (/ax-ax = 9.7 Hz, /ax-eq 3.S Hz) fur er indicated its pseudo-axial disposition, and structure (18) was proposed for the TiCU complex (equation S). 

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