Salts triazinium

More recently it has been found that 2-azonia-l,3-dichloroallene salts 11 react with carbodi-imides 12 to form the extremely moisture-sensitive dichlorodihydrotriazinium salts 13 which are stabilized by loss of alkyl chloride. The resulting 1,3,5-triazinium salts 14 are strong electrophiles which produce adducts with, for example, diisopropylcarbodiimide.431... 

Pyrrolo[ 1,2-b [l, 2,4[triazinium salt 30 was obtained (90CB2039) by the reaction of hydrazone 29 with the Vilsmeier reagent prepared from DMF and oxalylchloride (Scheme 9). 

Cyclization of hydrazone 38 with mercuric oxide and EDTA gave dihy-drotriazine 39 (87AP198). On the other hand, methyl hydrazone 38, under 4-electron withdrawal and neighboring group participation reacts with the same reagent to give lactam 40, a useful precursor for the synthesis of the pyrrolo[2,l-c]triazinium salt 41 by cyclization with perchloric acid (87AP258) (Scheme 12). 

Cyclization of diaminotriazines 1000 with carbon disulfide gave 1001, which were converted to triazinium salts 1003 and methylthio derivatives 1002 (82ZC219) (Scheme 185). 

It was shown that ring-opening reaction of the pyrido[l,2-A [l,2,4]triazinium salt 97 may easily occur with pyrrolidine to afford cis-trans and/or trans-trans triazinyl dienes 98 and 99 98 could be isomerized to -trans-i-trans isomer 99 (Equations 7 and 8) <1996JOC4423, 2001CPH(266)77>. 

Pyrido[l,2-3][l,2,4]triazinium salts 132 could be obtained from 131 with benzil either in the presence of TEA <2001CPH(266)77> or sulfuric acid <2003ARK155> (for example, diaminopyridines 131 are generally available from 2-aminopyridines 120 via N-amination with tosyl hydroxylamine (Scheme 14) <2003ARK155>). 

Phenylpyrido[l,2-3][l,2,4]triazinium salt 151 was investigated for its ability to intercalate DNA and for inhibition of reverse transcriptase. It showed moderate binding and inhibitory activity <2001AP269>. 

The last example for the synthesis of this ring system discussed in this section is somewhat different from the previous ones as it presents formation of a positively charged thiadiazolo[3,2-tf][l,3,5]triazinium salt as published by Okide 1994JHC535 the 2 amino 5 alkyl[l,3,4]thiadiazole 167 was reacted with l chloro l,3 bis(dimethylamino) 3-phenyl-2-azaprop-2-enylium perchlorate (a reagent which was synthesized by the same author earlier <1992JHC1551>) to give the quaternary salt 168 in moderate yield (45%) (Scheme 32). 

Two new syntheses to fused isoxazoles are worth mentioning. In a study for the synthesis of various related fused [l,3,5]triazinium salts, Okide described <1994JHC535> the conversion of 3-amino-5-methylisoxazole 223 with the iminium salt 224. The quaternary perchlorate salt 225 was obtained in medium yield (44%). A Russian research group <2004KGS592> reported that the isoxazole derivative 226 undergoes thermal cyclization when heated in xylene at higher temperature for an extended time, and the cyclized product 227 can be obtained in 53% yield. 

The arylfuro-fused pyrido[l,2-/ ][l,2,4]triazinium salt 179 undergoes reaction with methyl hydrazine to give the zwitterionic pyrido-fused pyridazino[3,4- ][l,2,4]triazine 31 as shown in Scheme 32 <2003ARK62, 1997CC757>. Nucleophilic attack of the hydrazine at the bridgehead results in the elimination of an enol that then allows ring closure via attack of the other hydrazine nitrogen onto the carbonyl of the keto tautomer. 

It was hoped that ring contraction of the triazinium salt 166 would give imidazo[2,l-6]thiazolium salts (167) on treatment with acid, but instead the free base of 166 was isolated on work-up of the reaction.159 Related pyridotriazine hydrobromides 168 underwent contraction in acid to give imidazopyridinium salts. 

Data on the structures of monocyclic dihydro- or hexahydro-1,2,3-triazines, on 1,2,3-triazine tV-oxides and 1,2,3-triazinones are not yet available. From studies on the one-electron reduction of the tetrahydro-l,2,3-triazinium salts (7) it was concluded that the heterocyclic ring is flexible and not planar (80LA285). No detailed information on the structure of 3-benzyl-l,5-diphenyl-l,2-dihydro-l,2,3-triazine-4,6(3//,5f/)-dione (8) or of the 6-hydroxy-4-oxo-l,4-dihydro-l,2,3-triazinium hydroxide inner salts (9) seems to be available. 

The mixed chloroacetic-acetic anhydride (538) with semicarbazones of aliphatic aldehydes or ketones (539) affords compounds (540) which cyclize to the 1,2,4-triazinium salts (541) (73ZOR834). 

The unexpected formation of the blue crystalline radical cation (97) from the reaction of triazinium salt (98) with tetracyanoethylene has been reported and the product identified by its EPR spectrum and by X-ray crystallography (Scheme 42).199 Carboxylic acids react with the photochemically produced excited state of N-t-a-phenynitrone (PBN) to furnish acyloxy spin adducts RCOOPBN. The reaction was assumed to proceed via ET oxidation of PBN to give the PBN radical cation followed by reaction with RCO2H.200 The mechanism of the protodiazoniation of 4-nitrobenzenediazonium fluoroborate to nitrobenzene in DMF has been studied.201 Trapping experiments were consistent with kinetic isotope effects calculated for the DMF radical cation. The effect of the coupling of radicals with different sulfur radical cations in diazadithiafulvalenes has been investigated.202... 

A typical example of such heterocyclization is the interaction of 3-phenyl-5-met-hoxy-l,2,4-triazine 182 with urea or A,A -dimethylurea in acetic or, better, in tri-fluoroacetic anhydride. The role of anhydride consists in converting starting molecule into a more electrophilic triazinium salt 183, which then reacts with a bifunctional nucleophile to form imidazotriazinone 184 (Scheme 54) (00MC58, 01JHC901). 

In fact, all other reactions of azinium cations with various 1,3- and 1,4-binucleo-philes represent AN AN processes resulting in the formation of stable di-aH-adducts, for example 218 or 220 (Scheme 64). Thorough investigations of these adducts, mostly derived from quinoxalinium and 1,2,4-triazinium salts, were carried out by Chupakhin and Charushin (for review see (88AHC(43)301, 04PAC1621)). They established that the di-adducts 218 and 220 have the corresponding mono-adducts 217 and 219 as their precursors. All mono- and di-adducts interconvert and depending on conditions any of them can be isolated. 

The tricyclic furo-fused 1,2,4-triazinium salt (74 X= O) reacts with nucleophiles such as sodium hydrogen sulfide, sodium diethyl malonate, or sodium ethyl cyanoacetate to yield the new ring systems thieno[2,3-e pyrido[l,2-Z>]-l,2,4-triazinium perchlorate (74 X= S) and cyclopenta(e]pyrido[ 1,2-b -1,2,4-triazines (75) [94CB1799]. 

Reaction of 1,2,4-triazinium salts with amides of acetoacetic acid results in 1,4,4a,5,7,7a-hexa-hydro-6/7-pyrrolo[3,2-e]-l,2,4-triazin-6-ones via the diaddition of bifunctional nucleophiles at the C-5 and C-6 positions of the 1,2,4-triazine ring (Equation (2)) <88TL1431>. 

Expansion of the furan ring is achieved by reacting compound (15) with hydrazine derivatives to give pyrido[l,2-6]pyridazino[3,4-c]-fl5-triazinium salts (20) (Scheme 4) <90CB1415>. 

In a similar manner, NH- and IV-alkyl-l,2,4-triazinium salts 38 react with acetoacetamides to afford pyrrolo[3,2-e][ 1,2,4] triazines (Scheme 48). 

Other cationic rings. Diazinium salts resemble pyridinium salts in their behavior. They form pseudobases with hydroxide ions which can disproportionate (e.g., 2-methylphthalazinium ion 217 2-methylphthalazin-l-one + 2-methyl-1,2-dihydrophthalazine) or undergo ring fission (e.g., 3-methylquinazolinium ion 218). 2-Alkyl-1,2,3-triazinium salts add nucleophiles at C(5) <2003S413>. 

Pyrido[l,2-7][l,2,4]triazinium salts 113 can be obtained from 112 with benzil in the presence of either base <2001CPH77> or sulfuric acid (Scheme 73) <2003ARK(xiv)155>. In an analogous reaction, 1,2-diaminopyridines 114 are transformed into 2,3,6-trioxopyridotriazines 115 by treatment with oxalyl chloride in the presence of triethylamine (Scheme 74) <1998SC3331, CHEC-III(12.03.2A4)237>. 

Also, 4-ClPhC(Cl)=N+=C(Cl)-4-ClPh SbClg 302 reacts with diaryl- or alkylarylcar-bodiimides to give labile 2,2-dichloro-l,3,5-triazinium salts 303. ° ... 

Synthesis of IV-monosubstituted 1,2,3-triazinium salts 13, from 1,2,3-triazines 12, and their reaction towards C-nucleophiles have been described <038413>. 

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