Phosphines azirines

In contrast to the well-defined photochemical behavior of 1-azirines the thermal reactions of these compounds have been studied less thoroughly (68TL3499). The products formed on photolysis of azirines can best be rationalized in terms of an equilibration of the heterocyclic ring with a transient vinylnitrene. Thus, products formed from the thermolysis of azirines are generally consistent with C—N cleavage. For example, the vinylnitrene generated from the thermolysis of azirine (149) can be trapped with phosphines (72CCS6S). 

Bromo-j3-nitrostyrene and triphenylphosphine in dry benzene gave the phosphonium bromide (47). Using methanol as the solvent, the rearranged product (48) was formed, possibly via an azirine intermediate. Substituted -bromo-/3-nitrostyrenes yield the phosphoranes (49) and a phosphonium salt. When the aryl group is electron-donating, the reaction follows a different course to form the styrene (50) by initial attack of the phosphine on halogen. 

The same research group synthesized also 2//-azirine-2-phosphine oxides 543 in a similar manner (equation 242). 

JOC6239, 96CHEC-2(1)1, 72CC565) and tris(dimethylamino)phosphine (76JOC543). Eor example, thermolysis of 2H-azirine 65 in the presence of triphenylphosphine resulted in the formation of phosphine adduct 68... 

A simple and efficient stereoselective synthesis of aziridine-2-phosphonate 781 and phosphine oxide 782 was achieved by diastereoselective addition of Grignard reagents to 277-azirine phosphonate 779 and phosphine oxide 780. Addition of benzenethiol and heterocyclic amines proceeded in an analogous manner to yield functionalized aziridines 783 and 784 (Scheme 188). 

Reactions of Isoxazoles. The kinetics of the isoxazole azirine rearrangement (336) -> (337) and those of the isoxazole oxazole transformation (338) (339) have been determinedPalladium(II) chloride-triphenyl-phosphine catalyses the cross-coupling of 4-iodo-3,5-dimethylisoxazole with styrene to yield the trans- compound (340). 3,5-Dimethylisoxazole can be lithiated in two stages, first at the 5-methyl group and then at the 3-methyl group. Isoxazoles add hypochlorous acid to form 4-chloro-2,3-dihydro-... 

It was shown that 1-azirines can serve as precursors to vinylnitrenes. A number of 1-azirines rearrange to indoles, most likely via vinylnitrene intermediates, upon heating. Two examples are known in which the nitrene formed during the thermolysis of azirines can be intercepted by tris(dimethy-lamino)phosphine or triphenylphosphine. ... 

The use of 2//-azirines, conjugated nitrosoalkenes and azoalkenes bearing phosphorus substituents in addition and cycloaddition reactions has been reviewed, focusing on methods giving aminophosphonate and amino-phosphine oxide derivatives. ... 

The regioselectivity is completely lost in the photocycloaddition of azirine 35 with diethyl vinyl phosphonate or dimethyl vinyl phosphine sulfide. The two isomers, 36 and 37 as well as 38 and 39, are found in equal quantities. 

Strong support for the existence of an azirine-vinylnitrene equilibration comes from work carried out by Nishiwaki and Padwa. Nishiwaki was able to show that the vinylnitrene generated from the thermolysis of azirine 273 can actually be trapped with phosphines, resulting in the isolation of adduct... 

A similar product was also isolated by heating azirine 126 in the presence of tris(dimethy lamino)phosphine. 

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