1,4-Bis(arylsulfonyl)-1,2,3,4-tetrahydropyridines in synthesis.: Highly regio- and stereoselective SN1′ and alkylation reactions

Reaction of lithiated beta-sulfonyl acetals with amino acid-derived N-tosylaziridines followed by acid-catalysed cyclisation gives enantiomerically pure 2-alkyl 1,4-bis(arylsulfonyl)-1,2,3,4-tetrahydropyridines 3 in good yields. These heterocyclic substrates react efficiently and highly stereoselectively with a range of carbon nucleophiles under Lewis acidic conditions to give the 1,2,5,6-tetrahydropyridine products of S(N)1' reaction, and undergo lithiation followed by completely stereoselective reaction at the 4-position with haloalkanes.