3,5,6,-Triphenyl-1,2,4-triazine, reduction

The Mitsunobu reaction was applied to the synthesis of pyrrolo[l,2-d [, 2,4]triazines from pyrrole derivative 71. Thus reduction of 71 gave alcohol 72, which on treatment with diethylazodicarboxylate and triphenyl phosphine gave 74 via the open chain intermediate 73. Hydrolysis of 74 gave 75 (84AG517) (Scheme 18). 

Electrochemical reduction of various 3,4-disubstituted-l,2,5-thiadiazole 1,1-dioxides (3,4-diphenyl- 10, phenanthro[9,10]- 51, and acenaphtho[l,2]- 53) gave the corresponding thiadiazoline 1,1-dioxides <1999CJC511>. Voltammetric and bulk electrolysis electroreduction of 3,4-diphenyl-l,2,5-thiadiazole 1-oxide 9 at ca. —1.5 V, in acetonitrile, gave 3,4-diphenyl-l,2,5-thiadiazole 8 (50%) and 2,4,6-triphenyl-l,3,5-triazine 54 (30%) (Equation 3) <2000TL3531>. 

Triphenyl-1,2,4-triazine (114) is reduced in aqueous media in two-electron steps the first reduction produces a mixture of isomeric dihydro derivatives, whereas reduction at the potential of the second step gives a mixture of 2,4,5-triphenylimidazole (115) and l,4,5,6-tetrahydro-3,5,6-tri-phenyl-1,2,4-triazine172 (116) [Eq. (85)]. 

The reduction of 3,5,6-triphenyl-1,2,4-triazine (114)346 to the dihydro derivative (first wave) and then to a mixture of a tetrahydro derivative (116) and... 

Reduction with zinc and acetic acid affords 1,2-dihydro-1,2,4-triazines (263) and imidazoles (264). The latter are secondary products, formed from (263) (57T103, 59CB2481, 63JCS1628). The compounds obtained by electrochemical reduction of 1,2,4-triazines have been shown to be 1,2-dihydro- (263) and 4,5-dihydro-l,2,4-triazines (265) (72CLU85, 72CJC1581). Reduction of l-methyl-3,5,6-triphenyl-l,2,4-triazinium iodide (266) with zinc and acetic acid affords 2,4,5-triphenylimidazole (267) and methylamine (63JCS1628). 

Atkinson and Cossey148 reported that the reduction of 2-methyl-5,6-diphenyltriazinium iodide (141) with potassium borohydride in methanol led to a tetrahydro-2-methyl-5,6-diphenyl-l,2,4-triazine. The ultraviolet absorption spectrum of this tetrahydro-l,2,4-triazine showed a maximum at 297 mfi (loge = 4.06). A similar reduction of l-methyl-3,5,6-triphenyl-l,2,4-triazinium iodide (142) gave a dihydro-1,2,4-triazine, the ultraviolet spectrum of which had maxima at 273 mft (loge = 4.46) and 410-420 m/x (loge = 3.62). No assignment of... 

At present, available data on dihydro-1,2,3-triazines is limited. Although reduction of 4,5,6-triphenyl-1,2,3-triazine (127a) with zinc in acetic acid or with hydrogen over palladium affords 3,4,5-triphenylpyrazole (130),209 the... 

Contrary to the reduction of other monocyclic 1,2,3-triazines (see Section 2.1.2.4.1.) reduction of 4,5,6-triphenyl-l,2,3-triazine with zinc in acetic acid (or catalytically) yielded 3,4,5-triphenylpyra-zole.88 The same compound was obtained when 4,5,6-triphenyl-l,2,3-triazine was treated with nonacarbonyldiiron.260... 

Photolysis of triphenyl-l,2,3-triazine 17z in diethylamine (DEA) and triethylamine (TEA) as solvents gives diphenylethyne as the main product and the diazocine 73, its valence isomer l,2,4,5,6,8-hexaphenyl-3,7-diazabicy-clo[4.2.0]octa-2,4,7-triene 74, and a product of reductive ring contraction of 17z, namely the 3,4,5-triphenylpyrazole 75, as minor products (Equation 10). To generate 75, the amine has to act as a sacrificial donor on the excited triazine and it is proposed that, after a series of consecutive electron and proton transfers (totalling four reduction equivalents), contraction of the six- to the five-membered ring occurs with release of ammonia <2002TF11>. 

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