1.3- diaza-2-azoniaallene salts 3+2 cycloaddition reactions

In a similar manner the l-aza-2-azoniaallene salts derived from coumarin and camphor react with diisopropylcarbodiimide to give the [2-1-3] cycloadducts. °i Also, l,3-diaza-2-azoniaallene salts 304 undergo the [2-1-3] cycloaddition reaction with diisopropylcarbodiimide or DCC to give 1,3,4,5-tetrasubstituted 4,5-dihydroten azolium salts. 305.11 ... 

The [3+2] cycloaddition reaction of the l,3-diaza-2-azoniaallene salts 28 with l,4-bis(4-bromophenyl)-l,4-di-t-butylbutatriene affords the cycloadduct 29, resulting from addition across the terminal double bond . 

The 1,3-dipolar character of triazaallenium salts, from now on referred to as l,3-diaza-2-azoniaallene salts, is evidenced by the many [3+2] cycloaddition reactions these types of compounds can participate in. The l,3-diaza-2-azoniaallene salts are generated in situ and trapped with suitable dipolarophiles. For example, l,3-diaza-2-azoniaallene salts undergo stereospecific [3+2] cycloaddition reactions with alkynes and olefins. However, they fail to react with isocyanates, isothiocyanates and azo compounds. Also, [3+2] cycloadditions to carbodiimides and cyanamides are observed. In contrast, nitriles fail to react. 1,3-Diaza-2-azoniaallene salts are obtained in the oxidation of 1,3-disubstituted triazenes with t-butyl hypochlorite. The resultant Al-chlorotriazenes react with antimony pentachloride to form the salts as reactive intermediates. Above —25°C, l,3-diaza-2-azoniaaUene salts disproportionate into diazonium salts and azo compounds. 

Table 7.1 Cycloaddition reactions of 1,3-diaza-2-azoniaallene salts with alkynes...

In the reaction of l,3-diaza-2-azoniaallene salts, R N=N+=NR, with dienes, such as butadiene and 2,3-dimethylbutadiene, mono [3+2] cycloadducts are obtained. From cyclooctatetraene a bis-cycloadduct was isolated. Also, allenes and higher cumulenes undergo [3+2] cycloaddition reactions with the same salts. With butatrienes, reaction proceeds across the terminal double bonds, while pentatetraenes react across the center double bonds. 

Table 7.2 13+2] Cycloaddition reactions of 1,3-diaza-2-azoniaallene salts with olefins ArN = N =NR + R R C=CR2R ------------------ ...

---