A novel reductive aminocyclization for the syntheses of chiral pyrrolidines: stereoselective syntheses of (S)-nornicotine and 2-(2′-pyrrolidyl)-pyridines
(S)-Nornicotine 2 was synthesized in four steps. A key step in the synthesis involved reductive aminocyclization of a 1, 4-ketoaldehyde with 2, 3, 4, 6-tetra-O-pivaloyl-β-d- galactosylamine 1 in the presence of sodium cyanoborohydride, diastereoselectively affording the corresponding stereoisomer 6 in 45% yield. The aminosugar moiety could be easily removed by acidic hydrolysis to furnish 2. The aminocyclization was further ...
