Pyrano l,2,4 triazines

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>. 

Reduction of the pyrano-l,2,4-triazin-3-one (132) using zinc powder in AcOH gave the dihydro compound (134) (85%). Analogous reduction of pyrano-l,2,4-triazin-3-thione (151) delivered com-... 

Electrochemical reduction of pyrano-l,2,4-triazin-3-ones (132) and (148) delivered the corresponding dihydro derivatives (134) and (153) in yields of 81% and 85%, respectively. Further electrochemical treatment of the compounds (134) and (153) provoked a ring contraction, leading to the pyranoimidazol-2-ones (154a,b) in 83% and 68% yield, respectively. Unexpectedly, attempted reaction of compounds (134) and (153) with NaBH4 in ethanol resulted in oxidation to the triazin-3-ones (132) and (148) (Scheme 7) (86JHC491). 

Pyrano-l,2,4-triazines (155a,b) reacted with methylmagnesium iodide giving the dihydro compounds (162a,b) in 9% and 65% yield, respectively <86JHC49l>. Similarly, compound (159) reacted with methylmagnesium iodide to deliver a 59% yield of compound (163) <90JHC1917>. 

Reaction of a mixture of chlorotriazine (149) and the isomer (150) with hydrazine hydrate delivered 3-hydrazinotriazine (192), isolated pure in a yield of 75%, together with the corresponding undesired hydrazinotriazine (193). Treatment of compound (192) with CuS04 in refluxing AcOH yielded 58% of the pyrano-l,2,4-triazine (135) (Scheme 11) <86JHC72l>. 

Diamino-(4//)-1,2,4-triazole hydrochloride (312) reacted in AcOH with 2,2,6-trimethyl-chroman-3,4-dione (311a) to give the pyrano-l,2,4-triazine derivative (194) (32%) (Equation (4))... 

The complex aziridine (356) underwent a rearrangement on acid hydrolysis to deliver 34% of the pyrano-l,2,4-triazine (357) <82JOC4465>. 

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. 

REACTIVITY OF SUBSTITUENTS ATTACHED TO RING CARBON ATOMS 7.17.7.1 2//-Pyrano 3,4-e -l,2,4-triazines... 

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