3 -methylisoxazolo pyridine reaction

Methylisoxazolo[5,4-. ]pyridine, 132, reacts with vinyl ether in a photocyclization reaction to give a mixture of mono- and bicyclic products, including a moderate yield of the dihydropyrrolo[3,2-3]pyridine derivative as one of three major products shown in Equation (65) <2002EJ04211>. 

The reaction of 2-acetyl-3-hydroxypyridine (441) with hydroxylamine 0-sulfonic acid afforded a 1 1 mixture of compound (442) and 2-methylisoxazolo[4,5-6]pyridine (443) (Equation (35)) <87H(26)292i). The formation of the oxazolo[4,5-6]pyridine (442) results from a Beckmann rearrangement. The reaction of the oxime (444) with hydroxylamine O-sulfonic acid also gave Beckmann rearrangement products, such as (445) and (446) as a 1 1 mixture (Equation (36)). 

Heating ( )-methyl l-oxide-2-pyridyl ketone oxime (482) in acetic anhydride at temperatures above 100°C initiated an exothermic reaction from which 3-methyl-3a-(3 -methylisoxazolo[4,5-b]pyridin-5 -yl)-3a//-[l,2,5]-oxadiazolo[2,3-a]pyridine (484) was isolated in 18% yield (Scheme 57) <86CPB4984>. If the reaction is carried out at a temperature less than 100°C, only the acetylated oxime (483) is isolated. Heating the (Z)-isomer in acetic anhydride at similar temperatures resulted only in the formation of the acetylated oxime. The structure of the product (484) was determined on the basis of two-dimensional COSY, DEPT, and 2D H-I3C chemical shift correlation experiments. The structure was also confirmed chemically via bromination which affords a mixture of the bromine adducts (485) and (486). Attempts to hydrolyze (484) under either acidic or basic conditions afforded only unchanged starting material. The formation of compound (484) from the TV-oxide (483) proceeds via a radical mechanism. This mechanism was elucidated by a study of the reaction... 

The reaction of (491( )) or (491(Z)) with sodium hypochlorite or lead tetraacetate gave 3-methylisoxazolo[4,5-6]pyridine 2,4-dioxide (492) in low yield <87H(26)292i> due to the low solubility... 

Treatment of 4-ethoxy-6-methylpyrimidine-l-oxide (602) with acetic anhydride at 25-35 °C in chloroform followed by the addition of diketene at <20°C caused an exothermic reaction from which was isolated 7-acetyl-4-ethoxy-2-methyloxazolo[4,5-c]pyridine (603) (22%) and 7-acetyl-4-ethoxy-3-methylisoxazolo[4,5-c]pyridine (604) (8%) (88CPB168). A plausible mechanism for the formation of the isomers (603) and (604) is shown in Scheme 77. Acetylation with acetic anhydride furnishes an initial intermediate, l,2-diacetoxy-l,2-dihydropyrimidine (605). Electrophilic attack by diketene at C-5 then yields an acetoacetyl intermediate (606). Ring-opening and recyclization of (606) then gives via intermediates (607) and (608) the pyridine (609). Compound (609), which is not... 

The photochemistry of ethyl esters of 2-oxo-carboxylic acids has the participation of both singlet and triplet excited states o. Triplet state lifetimes have been measured and the occurrence of Norrish type II splits in these molecules established. Other flash photolysis studies reported deal with the photoinduced tautomerism of 2-hydroxyphenazine °, 3-methylisoxazolo[5,4-b]pyridine °, and the photolysis of 4,4 -biphenylbiazide °. The tautomerism and phototautomerization of 4(3H)-pyridinethione has been examined theoretically by the infra red isolation technique . The effect of pressure on the photoinduced abstraction reaction of azanaphthalenes in mixed crystals of durene has also been studied. Photosolvolysis of arylmethanols also occurs in aqueous solutions of sulphuric acid . 

Condensation of 2-azido-P-phenethylamine with 4-chloro- or 4-nitrobenzaldehyde followed by reaction with diphenylketene in refluxing toluene gives the ketenimine 59 which undergoes an intramolecular [2tc + 27t] cyclisation to the azeto[2,l-6][l,3]benzodiazepines 60 <97T13449>. The method may be used also to synthesise azeto[2,l- )]quinazolines, the main thrust of the publication, but the tether cannot be increased further as the respective 8- and 9-membered ring systems could not be formed. UV irradiation of 4,6-diazido-3-methylisoxazolo[4,5-c]pyridine gives two products which have been identified and isoxazolo-... 

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