Synthesis and reactions of 1‐[1‐oxido‐2‐(3,4)‐pyridinyl]‐2‐methyloxiranes with nitrogen nucleophiles

Reaction of 2(3,4)‐pyridinecarboxaldehydes (5) with ethylidenetriphenylphosphorane afford a mixture of stereoisomers Z ‐( 6 ) and E ‐1‐[2(3,4)‐pyridinyl]‐1‐propenes ( 7 ). m ‐Chloroperbenzoic acid oxidation of 6 and 7 yields a 60:40 mixture of Z ‐( 8 ) and E‐1‐[1‐oxido‐2(3,4)‐pyridinyl]‐2‐methyloxiranes ( 9 ). The regiospecific reaction of Z ‐isomers 8a‐c with cyclic amines as piperidine give rise to threo ‐1‐hydroxy‐1‐[1‐oxido‐2(3,4)‐pyridinyl]‐2‐(1‐piperidino)propanes ( 10 ) while the E ‐isomer 9a yields erythro ‐ 11 . On tho other hand, the E ‐isomers 9b and 9c having 1‐oxido‐3(4)‐pyridinyl substituents afford erythro ‐ 12 resulting from attack by piperidine at C‐1 of the oxirane. Reductive deoxygenation using 10% palladium on charcoal and hydrogen gas effectively removed the N ‐oxide substituent from the threo ‐ 10 and erythro ‐ 11 β‐aminoalcohols. Dilute solution ir spectroscopy indicated the existance of strong intramolecular hydrogen bonding in the β‐aminoalcohols 10 and 11 . The assignment of relative configuration of diastereoisomers 10 and 11 was based on the magnitude of the vicinal coupling constant J where J threo is greater than J erythro.