摘要：

Ring cleavage of the N-oxides of N-methylazacycloalkanes by a thermal elimination reaction does not occur when the ring is six-membered and becontes progressively easier as the ring size is increased from seven to eight atoms. N-Methylpiperidine oxide gave no product from a cis beta-elimination reaction, while pyrolysis of the homologous N-methylhexamethyleneimine and N-methylheptamethyleneimine oxides led to the unsaturated hydroxylamines in yields of 53 and 79%, respectively. These results support a planar five-membered transition state for the amine oxide pyrolysis. The unsaturated hydroxylamines were converted to unsaturated and saturated secondary amines. The thermal decomposition of a mixture of he cis and trans isomers of N-methyl-alpha-pipecoline oxide formed the expected N-methyl-N-5-hexenylhydroxylamine as well as a saturated bicyclic product, formulated as cis-N-methyl-3-oxa-2-azabicyclo [3.3.01 octane. A possible mechanism for the formation of this product is presented. The cis and trans isomers of N-methyl-a-pipecoline oxide have been separated and characterized. Each Of the isomers has been pyrolyzed separately and only trans-N-methyl-a-pipecoline oxide formed the expected unsaturated hydroxylamine.

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