2- Azoniaallene cations

The 1,3-dipolar cycloaddition of 2-diazopropane with diarylideneacetones is temperature dependent, leading to mono-, di-, and tri-substitution products. The 1,3-dipolar cycloaddition of diazomethane and diazoacetate with 5-sulfur-2(5//)furanones provides a synthesis of furoisoxazolines. The 1,3-dipolar cycloaddition of 1-aza-2-azoniaallene cations with isothiocyanates produces 1,3,4-thiadiazolium salts and 1,2,4-thazolium salts. 

As evidenced from x-ray data, azoniaallene cations (61) adopt the less sterically demanding allylium valence tautomeric conformation (19) in accordance with Wurthwein s calculations <84CB3365,84JOC297l> which predict that this is the more stable conformation for amino substituted azoniaallene cations (Equation (1)). 

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