L-aza-2-azoniaallene salts

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 ... 

Jochims [134] and Hassan s [135] groups reported the efficient use of l-aza-2-azoniaallene salts 119 and 0-acetylated j6-D-glucopyranosyl isothiocyanate 89 for the preparation of glucopyranosylimino-l,3,4-thiadiazoles 121 and 122. These salts, prepared from chloroalkylazo derivatives 118 and antimony (V) chloride, can undergo 1,3-dipolar cycloadditions with multiple bonds-containing compounds, such as alkynes, alkenes, isocyanates, isothio-... 

The l-aza-2-azoniaallene salts are usually generated in situ and reacted at low temperatures with numerous dipolarophiles. The initially formed cycloadducts often undergo a 1,2-shift to form isomeric heterocycles. 

In the reaction of the l-aza-2-azoniaallene salts with ( )-3-hexene a single stereoisomer is obtained. However, in the reaction with allylcyanide, exclusive reaction of the nitrile group is observed. 

The [3-1-2] cycloaddition reaction of l-aza-2-azoniaallene salts with alkynes to give pyrazolium salts is a general reaction. The initially formed 3//-pyrazolium... 

The reaction of l-aza-2-azoniaallene salts derived from coumarins with alkynes does not afford cycloadducts but rather leads to intramolecular cyclization. In contrast, a [3+2] cycloadduct is obtained in 92 % yield (mixture of diastereoisomes, ratio 2 1) from the same salt in the reaction with norbornene. From the camphor salt 41 (R = 2,4,6-trichlorophenyl) and phenylacetylene a 53 % yield of the cycloadduct 42 is obtained . 

Also, RCH=N+=NR SbCle reacts with acetylenes and olefins to give the [3+2] cycloadductsSimilar cycloaddition reactions with alkynes and alkenes are also observed with l-(chloroalkyl)-l-aza-2-azoniaallene salts to give 43 examples are shown in Table 2.4 2. 

Azomethines undergo nucleophilic addition to l-aza-2-azoniaallene salts to give linear iminium salts. 

Heterocumulenes, such as isocyanates and carbodiimides also react with l-aza-2-azoniaallenes across the C=N bond to give [3+2] cycloadducts. For example, aliphatic and aromatic isocyanates add at -20 °C to l-aza-2-azoniaallene salts 50 to give 4,5-dihydro-5-oxo-3/f-l,2,4-triazolium salts 51 or the rearranged triazolium salts 52. ... 

In a recent theoretical study of the reaction of 1 -aza-2-azoniaallene salts, with isocyanates it was concluded that these reactions proceed in asynchronous but concerted pathways. The presence of chloro groups in the l-aza-2-azoniaallene salts, as well as methyl groups in the isocyanates, favor the cycloaddition reactions . 

In contrast to the isocyanate reaction with l-aza-2-azoniaallene salts, isothiocyanates react across their C=S bond in the [3+2] cycloaddition reaction to give 1,3,4-thiadiazolium salts. The initially formed [3+2] cycloadducts 53 undergo a 1,2-shift to give the isomeric adducts 54 °. 

Carbodiimides also undergo [3-1-2] cycloaddition reactions with l-aza-2-azoniaallene salts to give 4,5-dihydro-5-imino-li/-l,2,4-triazolium salts 56. The reaction proceeds stepwise, but the linear intermediate cannot be detected. 

In the [3-1-2] cycloaddition reactions of isothiocyanates with l-aza-2-azoniaallene salts the reaction also proceeds across the C>=S bond of the isothiocyanate to give 1,3,4-thiadiazolium salts in high yields 2. ... 

PhI(OTf)2 is an effective oxidant for the direct formation of bicyclic diazenium salts from a variety of linear hydrazone precursors. This oxidative cyclization is postulated to occur by the iodine(III)-mediated formation of an l-aza-2-azoniaallene salt intermediate. A direct intermolecular allylic amination has been achieved with up to 99% yields using metal-free conditions. The reaction employs a hypervalent iodine(lll) reagent as an oxidant and bistosylimide as a nitrogen source. Mechanistic studies including isotope labelling and Hammett correlation indicated that depending... 

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