Asymmetric synthesis of primary amines from alkenes and chiral chloronitroso sugar derivatives.

Abstract

A variety of alkenes 5 - 15, 38, 39 react with chloronitroso sugar derivatives 1 - 3 regioselectively at ambient temperature to give chiral hydroxylamines m 60 - 80% yield. In addition to these products of a formal ene reaction joined by a subsequent hydrolysis 2-substituted hydroxylamines 40 - 49 are also formed. The 2-substituted hydroxylamines 40, 41, 49 possess trans configurations exclusively. The product distribution is solvent dependent and susceptible to the addition of nucleophiles. The reactions employing the reagents 1 and 3 which are approximately mirror images in the vicinity of the chloronitroso function yield opposite enantiomers of the product. Their optical purity was determined by chemical reduction to the amine stage followed by the formation of diastereomeric camphorsulfonic- or Mosher acid amides and subsequent chromatographic or nmr spectrometric analysis. The optical purity for cyclic products was found in excess of 89% ee whereas acyclic alkenes yielded chiral amines in the range of 50 - 90% ee. Chemical degradation and comparison to authentic amino acids confirmed that in every case examined the reaction with the D-mannose derivative 1 yielded the S- configuration at the asymmetric carbon bearing the amino function. The formal ene reactions investigated thus provide another useful EPC synthesis of functionalized chiral amines in acceptable chemical yields and with a predictable stereochemical outcome.