98171-26-7Relevant academic research and scientific papers
Cycloadditions of 1,3,4-Oxadiazin-6-ones (4,5-Diaza-α-pyrones), 9. - Methyl 6-Oxo-5-phenyl-1,3,4-oxadiazin-2-carboxylate - Synthesis and Reactions with Norbornene, Norbornadiene, Cyclopropenes, Cyclobutene, and Benzvalene
Christl, Manfred,Lanzendoerfer, Ulrike,Groetsch, Maria M.,Ditterich, Elke,Hegmann, Joachim
, p. 2031 - 2037 (2007/10/02)
Methyl 6-oxo-5-phenyl-1,3,4-oxadiazin-2-carboxylate (7) was prepared by treatment of hydrazone 6 with dicyclohexylcarbodiimide.The reactions of 7 with norbornene and norbornadiene afforded the Diels-Alder adducts 8 and 9, respectively, which decomposed in solution at 20 deg C to give mainly the γ-oxoketenes 10 and 12 and small amounts of the β-lactones 11 and 13, respectively.The stable γ-oxoketenes 10, 12, and the bis(γ-oxoketene) 14 were obtained directly from solutions of 7 and the respective olefin.Cyclopropene, 1-methylcyclopropene, and cyclobutene were converted by 7 mainly into the oxepin derivatives 15, 17, 18, and the oxocin derivative 19, respectively.Benzvalene and 7 provided the tetracyclo2,8.04,6>octanone 21.In these reactions, small quantities of β-lactones were formed, too, which together with the β-lactones 11 and 13 give evidence for the dihydropyryliumolates 24 as intermediates in the thermal denitrogenation of the Diels-Alder adducts of 7, e.g. 8 and 9.
CYCLOADDITIONS OF 1,3,4-OXADIAZIN-6-ONES
Christl, Manfred
, p. 1 - 18 (2007/10/02)
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 ...
