Reactions of 1-Azirines

There has been a brief mention of 2-phenylazirine being prepared by the reaction of dimethyl oxosulfonium methylide (108) and benzonitrile (107).64 Due to the simplicity of this approach this method deserves further study. 

Leonard and Zwanenburg55 have treated azirine (26) with anhydrous perchloric acid and studied the reactions of the protonated azirine with acetone and acetonitrile. It is believed that protonated azirine ring 109 opens to cation 110 which then adds to the carbon-oxygen double bond or carbon-nitrogen triple bond to give the observed products (111 and 112). 

Koenig, H. Metzger, and K. Seelert, 100 (Hundert) Jahre BASF aus Forsch. 49 (1965) Chem. Abstr. 64, 17409 (1966). 

Treatment of azirine (26) with anilinium perchlorate resulted in destruction of the three-membered ring giving a-ammonioisobutyro-phenone anil perchlorate (116). The reactants have been postulated to proceed through aziridine (113), which rearranges through intermediates 114 and 115.50 

The treatment of azirine (92) with hydrazine perchlorate to give aminopyrazole (118)46 probably follows a mechanism similar to that for the reaction of anilinium perchlorate with azirine (26). However, now the intermediate 117 can cyclize to the pyrazole. 

The reaction of 2-phenyl-1-azirine with benzoic acid gave N-benzoylphenacylamine (120). Aziridine (119), which can rearrange to 120, is believed to be an intermediate in this reaction. 

---

The reactions of 1-azirines with ketenes and ketenimines represent non-concerted additions and are formally different from the additions to 47r-systems of dienes and 1,3-dipolar compounds (73JOC3466, 71CB2786). 

The 1-azirine ring also undergoes a number of reactions in which the heterocycle plays the role of the nucleophile. Although the basicity of the nitrogen atom in the azirine ring is much lower than in simple aliphatic amines, this system can still function as a nucleophilic reagent. One example of this involves the acid-catalyzed hydrolysis of 1-azirines to a-aminoketones (200) which represents a well-established reaction. In fact, in many reactions of 1-azirines where acid catalysis is used, formation of a-aminoketones is difficult to avoid (67JA44S6). 

The synthesis of metal-coordinated 1-azirines and the reactions of azirines induced by metals have opened a new area in the chemistry of this small ring heterocycle. Many of the reactions encountered bear resemblance to previously discussed thermally and photo-chemically induced reactions of 1-azirines. The reaction of a series of diiron enneacarbonyls in benzene results in coupling and insertion to give diimine complexes and ureadiiron complexes as well as pyrroles and ketones (76CC191). A mechanism for the formation of these products which involves initial 1,3-bond cleavage and generation of a nitrene-iron carbonyl complex as an intermediate was proposed. 

Dimerization reactions of 1-azirines with several transition metal complexes have been studied (76TL2589). Reaction of 2-arylazirines (289) with an equimolar amount of a Group VI metal carbonyl gives 2,5-diarylpyrazines (290) in good yield. On the other hand, these compounds are converted to 2-styrylindoles (291) with rhodium carbonyl compounds or with dicobalt octacarbonyl in benzene. 

One of the best known reactions of 1-azirines is the acid/catalyzed hydrolysis to aminoketones. Since the Neber reaction also accomplishes this same synthetic end, this reaction may appear to have little practical value. This is not the situation because with the Neber reaction there is no control over the aminoketone that will be obtained from a given ketone. For example, when oxime (127) derived from benzyl methyl ketone (126) is subjected to the Neber reaction aminoketone 128 is obtained.59 The amino function is substituted for the most acidic a-hydrogen. The isomeric aminoketone (132) that could not be prepared by the Neber reaction can be formed by the hydrolysis of 1-azirine (131). The synthesis of this 1-azirine has been accomplished from allyl benzene (129) through vinyl azide (130) using iodine azide.22... 

The reaction of 1-azirines with sodium borohydride has not been studied in detail, but one case was believed also to give the aziridine initially which ring-opened under the acidic reaction conditions.12... 

---