From Azirines

Azabicyclo[2.2.0]hexa-1,3,5-triene reactions, 7, 360 2-Azabicyclo[2.2.0]hex-5-ene reactivity, 7, 342 synthesis, 2, 371 2-Azabi cyclop. 1.0]hexene synthesis, 2, 371 2-Azabi cyclop. 1.0]hex-2-ene synthesis, 7, 67 2-Azabicyclo[k 1.0]hex-3-ene synthesis, 4, 258 6-Azabicyclo[k 1.0]hex-2-ene synthesis, 2, 305 Azabi cyclohexenes formation from azirines, 7, 58... 

In the reaction of with yiides generated from azirines, only the [6,6] adducts could be verified. For the reaction of diphenylnitrile ylide 282 (Scheme 4.51), which is generated by dehydrohalogenation of N-benzyl-4-nitrobenzimidoyl chloride with triethylamine, along with the closed [6,6] isomer 283 the formation of an open [5,6] bridged isomer was also claimed [321]. 

Carbenes are formed in a number of other similar reactions—for example, loss of carbon monoxide from ketenes or elimination of nitrogen from azirines—but these are rarely used as a way of deliberately making carbenes. 

An interesting application of PET mediated bond cleavage reaction from azirine 63 has been reported by Mattay et al. [67] for synthesizing N-substituted imidazoles (65) via the (3 + 2) cycloaddition reaction of resultant 2-azaallenyl radical cations with imines 64. Synthesis of pyrrolophane 3,4-dimethyl ester (68) has been reported recently [68] by the ring opening of 66 followed by inter-molecular cycloaddition with dimethyl acetylene dicarboxylate (67) as shown in Scheme 13. 

A further [3 4- 2)-cycloaddition process takes place when imines react with 2-azaallenyl radical cations (23) derived from azirines by photolysis (Scheme 4.2.10) [31, 32]. Yields of (24) are variable, e.g. 2,4,5-triphenyl-1-propyl- (87%), 4-butyl-1,5-dipropyl- (40%), 4-phenyl-1,5-dipropyl- (35%),... 

Exposure of an azirine to carbon monoxide in the presence of a catalytic amount of [Pd(PPh3)4] gives the bicyclic P-lactam (23) in reasonable yield. Attempts to synthesize monocyclic P-lactams from azirines has so far failed, but aziridines can be carbonylated to -lactams. )epending on the organome-tallic reagent used two different products can be obtained (Scheme 26). Using catalytic quantities of [Rh2(CO)4Ch] carbon monoxide inserts selectively into the more-substituted C—N bond, whereas using a stoichiometric amount of [Ni(CO)4] it is the less-substituted C—N bond that is carbonylated. ... 

Among the cycloaddition reactions which lead to imidazole products is the [3 + 2] cycloaddition of imines to 2-azaallenyl radical cations (derived from azirines by photolysis) which yields 1-substituted imidazoles <91AG(E)1336,93CB543). Similar addition of 2-azallyl anions (made by deprotonation of A-alkylated Schilf bases) to aromatic nitriles can give rise to either 3-imidazolines or imidazoles depending on the substitution pattern in the azaallyl species (229) <83CB492>. These reactions have been reviewed (Scheme 164) <90CHE1>. 

A number of examples of imidazole synthesis from azirines and aziridines have been included under other classifications (see Sections 3.02.8.1.l(iii) and 3.02.8.1.2(i),(ii)). 2/f-Azirines are intermediates in the rearrangement of oximino p-toluenesulfonates to aminoketones in the presence of bases, and with 2-acylphenols these azirines form imidazolones. 4//-Imidazoles (244) are formed when a 2-amino-3,3-dimethylazirine reacts with an acetamide (Scheme 181) <90CHE719>. 

Thioxo-2-thiazolines (334) can be synthesized by treatment of A(,iV-disubstituted thioamides (332) with dithiaphosphetane (333), an easily available sulfurating agent similar to the Lawesson s reagent. In turn, compounds (332) can be prepared from azirines and thiocarboxylic acids (Scheme 84) <87HCA1001>. 

Among the many reaction products obtained from hydrazones and osazones that offer promise to synthetic chemists are the carbenes generated from azirines and sulfonylhydrazono-1,5-lactones by irradiation.299 300... 

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