Azirines perchlorates

The protonated azirine system has also been utilized for the synthesis of heterocyclic compounds (67JA44S6). Thus, treatment of (199) with anhydrous perchloric acid and acetone or acetonitrile gave the oxazolinium perchlorate (207) and the imidazolinium perchlorate (209), respectively. The mechanism of these reactions involves 1,3-bond cleavage of the protonated azirine and reaction with the carbonyl group (or nitrile) to produce a resonance-stabilized carbonium-oxonium ion (or carbonium-nitrilium ion), followed by attack of the nitrogen unshared pair jf electrons to complete the cyclization. 

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). 

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 addition of some acids to 1 -azirines does not result in destruction of the three-membered ring. Leonard and Zwanenberg obtained aziridine (123) when 1-azirine (26) was treated with pyridinium perchlorate in pyridine.55 The structure of a similar product (23), prepared from Neber s azirine, was proposed by Cram and Hatch.12... 

A number of ring expansions of 3- and 4-membered heterocycles have been reported. Among the former is the reaction of 2H-azirines (43) or their salts with nitriles, a reaction first reported by Leonard. The reaction is promoted by perchloric acid ° or boron trifluoride,and is doubtless a... 

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