Pyrido triazinium

Nucleophilic substitution of compound 73 with 2-aminobenzimidazole in the absence of base gave pyrido[2,iy]-[l,2,4]triazinium iodide 67, which upon treatment with K2C03 afforded betaine 66. The latter compound could also be obtained by reaction of 73 with 2-aminobenzimidazole in the presence of base, whereas 66 could be converted to 67 by treatment with HI in methanol (Scheme 2) <1996T11349>. 

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>). 

The reaction of the pyrido-fused pyridazino[3,4-< ][l,2,4]triazinium compound 105 with secondary amines results in the ring-opening of the pyridine moiety to yield dienyl-substituted pyridazino[3,4-< ][l,2,4]triazines of which the pyrrolidine compound 106, shown in Scheme 15, is typical <2003ARK62, 1998AC0285, 1995JOC4919>. Compound 106 has been the subject of a detailed study and has been shown to react as a diene in the presence of fumaronitrile and A -phenylmaleinimide to give the Diels-Alder adducts 107 and 108, respectively <2003ARK62>,... 

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. 

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]. 

A novel pyrido[l,2-6]pyrrolo[2,3-e]-a -triazine (19) is produced when compound (15) is treated with ammonia ammonia attacks the C-lOa carbon and causes ring opening to give the triazinium derivative (18 Nu = NH2) and the amine substituent is then able to react with the carbonyl group of the benzoyl substituent to give the cyclized product (19) in high yield. 

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>. 

Reaction of 2,3-diaminopyridine with l-ethyl-3-morpholino-l,2,4-triazinium tetrafluoroborate gave a mixture of the cyclic adducts (381), which upon treatment with KMn04-acetone afforded pyrido[2,3-6]pyrazine (382) (Equation (55)) <87KGS280>. 

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>. 

Batori, S., Messmer, A., Timpe, H. J. Condensed as-triazines. Part XI. Photoinduced fragmentation of pyrido[2,1-f]-as-triazinium-4-olate and its benzolog. Mechanism of Curtius rearrangement. Heterocycles, 32, 649-654. 

Tricyclic furo[2,3-e]pyrido[l,2-fr][l,2,4]triazinium salt 612 underwent ring transformation by reaction with carbon nucleophiles. Thus, the sodium salt of 1 generated from reaction of 1 and sodium hydride in acetonitrile, was treated with 612 to give 7-benzoyl-8,9,10,ll-tetrahydro-9,9-dimethylindenoll,2-eJpyrido[l,2-frJl,2,4-triazin-ll-one (94CB1799), which because of the enhanced delocalization of the n electronic system, it existed in two equilibrium forms 613 and 614 (Scheme 132). 

Dichloroazacyanines, which can be prepared from dialkyl cyanamides with phosgene imini-um chloride, cyclize with pyridin-2-amine to form 2,4-bis(dimethylamino)pyrido[1,2- ]-l,3,5-triazinium perchlorate in 75% yield.489... 

Diaminopyridinium iodide undergoes reaction with ethyl aceto-acetate and acetylacetone to form somewhat unexpected products, the pyrido[l,2-a]pyrimidine derivatives 33 and 34, respectively.154 The initial step has been shown to be decomposition of 1,2-diaminopyridinium iodide to 2-aminopyridinium iodide which undergoes condensation with [i-dicarbonyl compounds. The reaction of 1,2-diaminopyridinium salt with 1,2-dicarbonyl compounds gives pyrido[ 1,2-A] [1,2,4]-triazinium salts 35.161... 

Regioselectivity of methylation reactions of pyrido[2,l-/][l,2,4]triazinium-4-olates and 4-thiolates (obtained from the 4-olates with P2S5) (68 X = 0 or S) was studied <88JHC437, 90JHC1673>. With methyl iodide, 3-NMe and SMe derivatives, respectively, were exclusively formed. Mixtures of (69) and (70) were obtained with trimethyloxonium fluoroborate (Equation (4)). Phenylation of the 4-olate with diphenyliodonium tetrafluoroborate gave a 3-NPh derivative, whereas phenylation of the 4-thiolate afforded 4-SPh derivatives of type (70 X = S)... 

Photolyses of pyrido[2,l-/][l,2,4]triazinium-4-olates and a [l,2,4]triazino[6,l-a]isoquinolinium-4-olate in methanol gave 2-pyridinecarboxamide and 1-isoquinolinecarboxamide, respectively... 

Methylation of the l,2-dihydro-2-hydroxy pseudo base (90) with trimethyloxonium hexa-fluorophosphate led to the formation of the 1-methyl derivative (91) (Equation (10)) <92T8459>. Compound (92) was cyclized on treatment with polyphosphoric acid to the furo[2,3-e]pyrido[l,2- ][1.2,4]triazinium salt (93) (Equation (11)) <89CB1935>, which proved to be a versatile starting material for 2-methoxy- and 2-pyrrolidinopyrido[l,2-h][l,2,4]triazines <89CB1935>, and also for pyridazino-fused derivatives <90CB1415>. 

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