Synthesis and x-ray analysis of dihydro-1,2,4,5-trioxazine. Evidence of a stepwise mechanism for the [3 + 3] cycloaddition of carbonyl oxides with nitrones
摘要:
Carbonyl oxides, derived by ozonolysis of vinyl ethers, readily undergo [3 + 3] cycloaddition reactions with nitrones affording dihydro-1,2,4,5-trioxazines in fair to excellent yield. The structures of dihydro-3,5,6-triphenyl-1,2,4,5-trioxazine (5f) and dihydro-3-cyclohexyl-5-methyl-6,6-diphenyl-1,2,4,5-trioxazine (5t) were unambiguously determined by X-ray analysis. Ozonolysis of 1-cyclohexyl-2-methoxyethene in the presence of either (E)- or (Z)-alpha-(4-methylphenyl)-alpha-phenyl-N-methylnitrone gave a 1:1 mixture of two stereoisomeric cycloadducts. This result, in conjunction with the structure of the relevant 5t, suggests that the [3 + 3] cycloaddition proceeds by a stepwise mechanism.
Primaryamines were prepared from alkyl halides or olefinic compounds by the use of N-benzylhydroxylamine and 2-fluoro-1-methylpyridinium p-toluenesulfonate.
Hypervalentiodine compounds are viable reagents for the oxidation of N,N-disubstitutedhydroxylamines to the corresponding nitrones, with IBX performing best. The procedure is very simple and user-friendly and affords the target compounds with high efficiency and regioselectivity, highlighting IBX as the reagent of choice for preparation of aldonitrones from nonsymmetric hydroxylamines. Evidence for
A new green method for the preparation of nitrones through the aerobicoxidation of the corresponding N,N‐disubstituted hydroxylamines has been developed upon exploring the catalytic activity of a diruthenium catalyst, that is, [Ru2(OAc)4Cl]), in aqueous or alcoholic solution under mild reaction conditions (0.1 to 1 mol % catalyst, air, 50 °C) and reasonable reaction times. Notably, the catalytic activity