98171-29-0Relevant academic research and scientific papers
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 ...
