Azines reaction with dipolarophiles

Azine approach. 4,5-Dihydro-6//- 1,2-oxazine 2-oxides undergo 1,3-dipolar cyclo-addition reacting with appropriately substituted alkenes and alkynes to form isoxazolo-[2,3-Z>][l,2]oxazines. With styrene as the dipolarophile in the reaction with the oxazine (87), the product (88) with cis methyl and phenyl groups is formed. With acrylonitrile and methyl acrylate, some trans isomer is formed, but the cis isomer is predominant. The rings are always c/s-fused (77IZV211). 

Theoretical explorations of the formation of azines (38) from the addition of methylene- or dimethyl-carbene to their diazirine precursors have been reported. These reactions, which proceed through an ylide intermediate (39), show no enthalpy barriers, the activation energy being only a function of entropy factors. Dichlorocarbene has been shown to form ylides with diazines these ylides react further with dipolarophiles to give 1,3-dipolar cycloaddition products. ... 

Azine A-oxides and azine A-imides undergo a deep ring transformation on interaction with various dipolarophiles. Thus, fervenulin-4-oxides (423) react with DMAD to afford derivatives of pyrrolo[3,2-first step of the reaction is assumed to involve the formation of cycloaddition products (424) which transform by subsequent multi-stage process into (425) (79JOC3830). 

Azine approach. Enamines when used as dipolarophiles with nitrile oxides form isoxazoles. With cyclic enamines such as (89) fused isoxazoles are formed the nitrile oxide in this reaction is generated in situ from benzhydroxamoyl chloride (64JOC1582). 

---