Methanol → 1-methyl-3-(alpha,alpha,alpha-trifluoroacetyl)-1,6-dihydropyridine-O-methyl oxime

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Reaction Conditions

Reaction Steps

1-Methyl-3-(α,α,α-trifluoroacetyl)pyridinium-O-methyl oxime iodide (D10) (10.4 g, 0.030 mol) in a 1:1 mixture of water and methanol (20 ml) was added dropwise to a suspension of sodium borohydride (2.17 g, 0.057 mol) in 1:1 water/methanol (40 ml) at 0° C. The reaction mixture was maintained at 0° C. for 0.5 h then warmed to room temperature and stirred at this temperature for 1 h. The mixture was diluted with water (40 ml) and extracted with chloroform (3×100 ml). The combined organic extracts were dried (Na2SO4) and evaporated to give a gum which was chromatographed on silica using ethyl acetate as eluant to afford in order of elution 1-methyl-3-(α,α,α-trifluoroacetyl)-1,6-dihydropyridine-O-methyl oxime (3.65 g, 55%) as a mobile oil which rapidly became highly coloured and 1-methyl-3-(α,α,α-trifluoroacetyl)-1,2,5,6-tetrahydropyridine-O-methyl oxime (1.52 g, 23%) as a pale yellow mobile oil which consisted of a 14:1 mixture of E and Z isomers. A portion of this material (0.5 g, 0.0023 mol) was taken-up in benzene and irradiated (254 A) for 4 days. The benzene was removed in vacuo and the residue was filtered through silica using ethyl acetate as eluant to give a 3:1 mixture of E and Z isomers (0.25 g). Addition of oxalic acid gave a solid which was recrystallised twice from methanol/acetone to give the E isomer (0.12 g) m.p. 140°-143° C. The combined mother liquors were evaporated to give a solid which was a 1:1 mixture of E and Z isomers (E4) m.p. 103°-110° C.

Provenance & Evidence