Pyrano triazines

A series of 3-aryl-5,8-dihydro-6,6,8-trimethyl-5,8-ethano-6H-pyrano [4, 3-e][l,2,4]triazine-4-oxides 193 was prepared (79JHC1389) by boiling a mixture of 192 and trimethyl orf/io-arylates. The effect of substituents on the chemical shifts of their 13C NMR spectra was studied. 

Alkylation of pyrano[2,3-z7]-l,2,3-triazine 203 with a number of electrophiles in 15% potassium hydroxide/acetone solution gave the substituted triazines 204 in a remarkably consistent 55% yield (Equation 18) <2003MI1061>. 

Nitrosation of pyranocarboxamide 255 with sodium nitrite in acetic acid gave the pyrano[2,3- -1.2,3-triazine 256 (Equation 27) <2003MI1061>. 

A new, simple, synthesis of 2,4-diaryl-l, 3,5-triazines is shown in Scheme 1. It arose from an attempt to obtain the pyrano[4,3-rf]pyrimidine system by reacting aryl amidines with the 3-methoxymethylenedihydropyran-2,4-dione (1 X= CH2). As well as the desired products, diaryl-I,2,3-triazines were obtained in 30-40% yield. The use of 5-methoxymethylene-2,2-dimethyl-l,3-dioxan-4,6-dione (1 X= 0)(derived from Meldrum s acid) gives the triazines in better yield (> 50%). It was also observed that 3-methoxymethylenefuran-2,4-dione reacted with 5-methylisothiouronium bromide to yield 2,4-bismethylthio-l,3,5-triazine [95M99]. 

Interaction of 8a with ethylchloroacetate in methanolic sodium methoxide leads to cyclocondensation with elimination of EtOH and HC1, affording the triazine-3,14-dione derivative (14), while 8a was reacted with alcoholic CS2-KOH to give 14-methyl-2,3-dihydro-13-oxo-2H,13H,14H-[l]Benzopyrano [3/,4/ 5/,6/]pyrano[3,2-e]-[l,2,4]triazolopyrimidine-2-thione (15) (Scheme 5). 

The pyrano-l,2,4-triazine derivative (127) was converted into the saturated system (128) in a three-step sequence of acetylation, hydrogenation, and subsequent deacetylation. The isomeric triazine (129) was similarly transformed into the saturated counterpart (130) <82Mi 7i7-oi>. 

Reduction of the pyrano-l,2,4-triazin-3-one (131), as a mixture with the isomer (132), gave the dihydro compounds (133) and (134) in an overall yield of 60% <85JHC33>. 

The pyrano-l,2,4-triazine (135) reacted with methylmagnesium iodide to deliver compound (143)... 

A mixture of pyrano-l,2,4-triazin-3-one (131) with the isomeric triazin-3-one (132) was methylated using KOH and Me2S04 to give a mixture of the corresponding methylated derivatives (147) and (148) (86%) <85JHC33>. 

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