Mild Cleavage of N–O Bond of 3,6-Dihydro-1,2-oxazines by Condensation of Aldehydes in Aqueous Media
作者:Cyrille Kouklovsky、Gilles Galvani、Robert Lett
DOI:10.1055/s-0034-1380533
日期:——
The nonreductive cleavage of a model 3,6-dihydro-1,2-oxazine by condensation of 2,2-dimethoxyacetaldehyde under aqueous conditions is investigated. Depending on the pH of the solution, the reaction leads either to the N-acylated 1,4-amino alcohol or to the corresponding stable hemiaminal. The formation of the former is believed to proceed through iminium to oxaziridine rearrangement and not through enamine formation, as confirmed by the use of nonenolizable aldehydes. This procedure allows a very mild, nonreductive cleavage of N-O bonds.
Diels-Alder and ene reactions of nitrosyl hydride and nitrosoformaldehyde
作者:Harry E. Ensley、Shivkumar Mahadevan
DOI:10.1016/s0040-4039(00)99215-3
日期:1989.1
Diastereoselective hetero-diels-alder cycloaddition of a C-nitroso compound prepared starting from a homochiral imidazolidin-2-one
By Swern oxidation of the hydroxamic acid 3, prepared from the homochiral imidazolidin-2-one 1, the transient C-nitroso derivative 4 is obtained, and its cycloaddition to either cyclohexadiene or cyclopentadiene proceeds with high diastereoselection, owing to the conformational stability of 4. The stereochemical outcome of the reaction is determined from H-1 NMR data and further confirmed by the specific rotation value of 7, obtained by cleavage of the major cycloadduct 5a.