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• 100-42-5 styrene 
• 98171-26-7 6-Oxo-5-phenyl-6H-[1,3,4]oxadiazine-2-carboxylic acid methyl ester 

Relevant academic research and scientific papers

Cycloadditions of 6H-1,3,4-oxadiazin-6-ones (4,5-diaza-α-pyrones). Part 16. 4-Substituted and 4,5-disubstituted methyl 3-phenyl-α-pyrone-6-carboxylates from γ-oxoketenes via α,δ-dibromo-δ-lactones

The addition of bromine to the γ-oxoketenes 4, 10 and 22 and the elimination of two equivalents of hydrogen bromide from the resulting α,δ-dibromo-δ-lactones 5, 12 and 23 to give the α-pyrones 7, 19 and 20, respectively, are described. Since the isolation of neither 4, 10 and 22 nor 5, 12 and 23 proved necessary, the α-pyrones have been prepared in one-pot procedures from methyl 6-oxo-5-phenyl-6H-1,3,4-oxadiazine-2-carboxylate 6.

Cycloadditions of 6H-1,3,4-Oxadiazin-6-ones (4,5-Diaza-α-pyrones), 12. - Dieckmann Condensations without Bases

Prepared by treatment of methyl 6-oxo-5-phenyl-6H-1,3,4-oxadiazine-2-carboxylate (1) with norbornene, norbornadiene, and styrene, respectively, the γ-oxoketenes 2, 5, and 7 were allowed to react with methanol.Inter alia, the semiacetals 3, 6, and 10 of 1,2-cyclopentanedione derivatives were formed.The identity of 3 has been established by an X-ray structure analysis.The pathway to these compounds seems to be closely related to the mechanism of the Dieckmann condensation.By using methanol, it has been shown that the semiacetal methoxy group underwent an intramolecular migration.Methanol was eliminated from semiacetal 10 by chromatography on silica gel with formation of the enol 11.In addition to 3 and 10, the dimethyl adipates 4 and 9 were observed as the expected methanolysis products of the γ-oxoketenes 2 and 7, respectively.The diesters 9 were obtained on a second route from 7.Treatment of 7 with trifluoroacetic acid and subsequent hydrolysis gave rise to the monoesters 12, which were converted into the diesters 9 by conventional esterification. Key Words: 1,3,4-Oxadiazine-2-carboxylate, methyl 6-oxo-5-phenyl- / Diels-Alder reactions / Ketenes, γ-oxo- / 1,2-Cyclopentanedione derivatives / Adipic acid, substituted 2-oxo- dimethyl esters

CYCLOADDITIONS OF 1,3,4-OXADIAZIN-6-ONES

From substituted 2-oxoethanoic acids and acylhydrazines the corresponding hydrazones 1 are prepared, which can be cyclized to give the title compounds 2.The reactions of 2 with activated alkynes (yneamines, cyclooctyne, dehydrobenzene) proceed as -cycloadditions and result in the formation of α-pyrones after loss of nitrogen.Reactions of this type are possible also intramolecularly, if the oxadiazinones (2r-u) contain a properly located alkyne group.Oxadiazinones 2 undergo Diels-Alder cycloadditions with a variety of olefins.Diaryloxadiazinones react with alkenes which are activated by ring strain (cyclopropene, cyclobutene, trans-cyclooctene), by a high-lying HOMO (benzvalene, styrene, enamines), or by the factor > in the case of norbornene.The methyl phenyloxadiazinonecarboxylate 2p is highly reactive and takes up even 1-octene and cyclohexene.The primary adducts of type 54 readily extrude nitrogen to give 4,5-dihydropyrylium-2-olates (60) as most probable but not observed intermediates.In one case the expected -cycloadduct, namely 26, could be isolated.The ultimate products are generally derived either from 60 or from γ-keto ketenes 53, which are believed to be in equilibrium with 60. γ-Keto ketenes 53 have been detected with many systems and are stable in certain cases.When diphenyloxadiazinone, 2a, was treated with norbornene, norbornadiene, cyclopentene, trans-cyclooctene, or styrene, enol lactones of type 63 were isolated, which are considered to be formed from the intermediate dihydropyryliumolates 62 by a suprafacial -H shift.Cyclopropenes and cyclobutene transform oxadiazinones 2 to α,β-unsaturated seven-membered enol lactones 64-67 and eight-membered enol lactone 69, respectively.These products are believed to be the result of valence isomerizations of the corresponding dihydropyryliumolates (74, 75).Enamines behave exceptionally in that they can convert the oxadiazinones 2 into products not derived from the -cycloaddition (e.g. 82, 88, 89), although the latter process is dominating in most examples investigated to date.The compounds obtained from the usual -cycloadditions are amides of α,β-unsaturated δ-oxo acids (78, 80) and α,β-unsaturated δ-amino-δ-lactones (81).The former are believed to arise from α-amino-γ-keto ketene intermediates (76) by -amino migrations, whereas the formation of the latter (81) can be rationalized in two different ways, one being a -amino migration starting from the possible intermediates 85 (4-amino-4,5-dihydropyrylium-2-oltes).Cyclobutanone derivatives 50 and 52 and cyclopentanone derivatives 16 originate from γ-keto ketenes generated from cis,trans-1,5-cyclooctadiene, o-vinylstyrene, and benzvalene, respectively.In these cases, intramolecular cycloaddition of the ketene functionality occurs across either the CC double bond or the strained bicyclo-butane sigma bond, respectively.Intermolecular -cycloadditions of the corresponding γ-keto ketenes with cyclopentadiene, 2,3-dihydrofuran, and ...