Synthesis and [3+2] Cycloadditions of 3-Bromo-5,6-dihydro-4H-1,2-oxazine N-Oxides

Abstract

A number of 3-bromo-5,6-dihydro-4H-1,2-oxazine Noxides have been synthesized and subjected to [3+2] cycloaddition with alkenes affording various types of products: 3-vinyloxazolines, isoxazoline N-oxides, and 3-functionalized 1,2-oxazine N-oxides.

Developments and applications of α-bromonitrostyrenes in organic syntheses

“…Bromonitrostyrenes can be applied for the construction of 3bromo-5,6-dihydro-4H-1,2-oxazine N-oxides (Scheme 11). 40 An alkene was used as a coupling partner and the cyclization reaction was performed in the presence of SnCl bicycle[3,2,1] octane of 1,2-diones 25 from nitroalkenes and 1 1,2cyclohexadione 24 (Scheme 12). 41 a-Bromonitroalkene 1 in a domino Michael-Henry reaction with diketone 24 can furnish product 25 with two syn and anti isomers.…”

“…Bromonitrostyrenes can be applied for the construction of 3-bromo-5,6-dihydro-4 H -1,2-oxazine N -oxides ( Scheme 11 ). 40 An alkene was used as a coupling partner and the cyclization reaction was performed in the presence of SnCl 4 or TiCl 2 (O i Pr) 2 as a Lewis acid catalyst. (4 + 2)-Cycloaddition of alkene to bromonitrostyrene was sensitive to the reaction conditions, where an increase in temperature or time led to 3-chloro-1,2-oxazine N -oxide as byproduct.…”

Bromonitroalkenes as efficient intermediates in organic synthesis

“…By using an excess amount of alkene in the reaction with 157 under base-free conditions, the N -oxides hydrolyzed to give lactones 160 . 56…”

3-Halo-5,6-dihydro-4H-1,2-oxazine N-oxides as synthetic equivalents of unsaturated nitrile oxides in the [3 + 2]-cycloaddition with arynes: synthesis of substituted 3-vinyl-1,2-benzisoxazoles

“…Following previous studies on the [4 + 2]-cyclofragmentation of 1,2-oxazine N -oxides to unsaturated oxime derivatives, 14 as well as reactions of 1,2-oxazine N -oxides with arynes, 15 we envisioned 3-halo-substituted 1,2-oxazine N -oxides as viable surrogates of unsaturated nitrile oxides. It relies on the possibility of base-promoted cyclofragmentation/elimination of HBr (Scheme 1, (4)).…”