5-Iodo 1,2,3-triazoles

We have recently reported that the air-stable and hydrosoluble iminophosphorane copper(I) complex 6 is also active in CuAAC of 1-iodoalkynes in aqueous media, under mild and aerobic conditions according to click laws and displaying a broad substrate scope and functional compatibility [29] (see Scheme 15.8). It is important to note the following catalytic features (i) catalyst 6 was the first example of an isolated and crystallographically characterized copper(I) catalyst active for cycloaddition of 1-iodoalkynes with azides, to give 5-iodo-1,2,3-triazoles exclusively, (ii) The presence of a free thio moiety in the substrate does not deactivate the catalyst, a fact generally observed in CuAAC for functionalized substrates... 

The 4- and 5-amino-l,2,3-triazoles are diazotizable, e.g. the diazonium salt from 4-aminotriazole-5-carboxamide with potassium iodide gives the 4-iodo derivative, and that from 4-amino-l,5-diphenyltriazole gives 1,5-diphenyltriazole in ethanol (74AHC(16)33). 

A related iodo-promoted cyclization of the analogous triazole derivative 343 has been reported to give a more complex reaction mixture, where compounds 32 and 44 have been characterized (Equation 65) <2004GHE1207>. 

The iodo-promoted cyclization reaction of 4-allyl-5-phenyl-l,2,4-triazole-3(47/)-thione 344 gives a mixture of compounds 31 and 345 (Equation 66) <2004CHE1077>. 

Halogenation of w-triazole and several monomethyl and dimethyl derivatives has been studied.Bromination of v-triazole gives the 4,5-dibromo derivative with an excess of sodium hypobromite, a 1,4,5-tribromo derivative can also be isolated. Attempted chlorination gave the hydrochloride salt instead, although 1-methyltriazole gives a 4-chloro derivative. A 1-iodo derivative, which rearranges on heating to the 4-isomer, is obtained with iodine. 

Displacement of nitrogen from diazonium salts derived from 4- or 5-aminotriazoles can be achieved in the same manner as for other aromatic diazonium salts for example, diazotization of 4-amino-triazole-5-carboxamide and reaction with iodine and potassium iodide gives the 4-iodo derivative. ... 

Two products were isolated 5-Iodo-l,3-diphenyl-l,2,4-triazole (47/39%) and 3-iodo-5-phenyl-1,2,4-triazole (10/37%). 

When heated, the relatively stable 1-iodo-l,2,3-triazoles rearrange to the 4-isomers (70ZC220). 

Palladium catalyzed cyclization of l-iodo-2-((propa-l,2-dienyloxy)methyl)benzene 150 occurs with concomitant anion incorporation to furnish 4-substituted-l//-isochromenes 151 (Scheme 49) <1998TL435, 2000J(P1)3799>. In the presence of norbornadiene 152, the initially formed azide can undergo a further 1,3-dipolar cycloaddition reaction and fragmentation to give l-((l//-isochromen-4-yl)methyl)-l//-l,2,3-triazole 153 (Scheme 49) <1998TL435, 2001T7729>. 

The halogen metal exchange reaction between 7-bromo or 7-iodo-3-phenyltriazolopyrimidine 165 and butyllithium in iV,N,N, N -tetra-methylethylenediamine afforded the 7-lithio compound 166, whereas a similar reaction with the 7-chloro derivative 165 (R = H) gave the ring-fission product, 5-amino-l-phenyl-l//-l,2,3-triazole-4-carbonitrile 169 (91 CPB2793). Reaction of 166 with electrophiles such as benzaldehyde and ketones gave 170 and 167 respectively, together with 7,7 -bis[3-phenyl-3//-1,2,3-triazolo[4,5-d]pyrimidine] 168 (Scheme 34). 

The reaction of 3-iodo-l-methyl-l,2,4-triazole with 2-methylbut-3-yn-2-ol (75IZV690) has been used to prepare 3-ethynyl-l-methyl-l,2,4-triazole (117 Scheme 38) and the isomeric 5-ethynyl-1-methyl isomer from the corresponding iodotriazole. 

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