Scope and Mechanism of Intramolecular Aziridination of Cyclopent-3-enyl-methylamines to 1-Azatricyclo[2.2.1 .02,6]heptanes with Lead Tetraacetate.

A series of seven cyclopent-3-en-1 -ylmethylamines bearing one, two, or three methyl substituents at the C2, 03, C4, or Cα positions, including the unsubstituted parent, was accessed by ring-closing metatheses of α,α-diallylacetonitrile (or methallyl variants) and α,α-diallylacetone followed by hydride reductions or reductive amination, or by Curtius degradationsof α,α-dimethyl- and 2,2,3-trimethylcyclopent- 3-enylacetic acids. Oxidation of the primary amines with Pb(OAc)4 in CH2Cl2, CHCl3 or benzene in the presence of K2CO3 effected efficient intramolecular aziridinations, in all cases except the α-methyl analogue (16), to form the corresponding 1 -azatricyclo[2.2.1 .02,6]heptanes, including the novel monoterpene analogues, 1 -azatricyclene and the 2-azatricyclene enantiomers. The cumulative rate increases of aziridination reactions observed by 1H NMR spectroscopy in CDCl3 resulting from the presence of one or two methyl groups on the cyclopentene double bond, in comparison to the rate of the unsubstituted parent amine (1 :17.5:>280), indicate a highly electrophilic intermediate as the nitrene donor and a symmetrical aziridine-like transition state. A mechanism is outlined in which the amine displaces an acetate ligand from Pb(OAc)4 to form a lead(lV) amide intermediate RNHPb(OAc)3 proposed as the actual aziridinating species. [ABSTRACT FROM AUTHOR]