rnDie durch Addition von N-Alkyl-hydroxylaminen an Acetylendicarbonester darstellbaren Nitrone 3 liefern mit Acetylendicarbonester oder Propiolester thermisch instabile Addukte 2 bzw. 16. Aus 2 entstehen bereits bei Raumtemperatur durch Cope-Umlagerung Enamin-ketone 5, die sich als die Zwischenstufe der Hantzschschen Pyrrolsynthese erweisen. Eine Nacharbeitung der Addition yon N-Phenyl-hydroxylamin an Acetylendicarbonester fuhrt zur Revision der in der Literatur angegebenen Struktur fur das 2:2-Addukt (39a statt 27). rnDas bei der Addition von N.N-Diathyl-hydroxylamin an Acetylendicarbonester sich bildende N-Oxid 1 zerfallt u. a. nach Art eines Cope-Abbaus in Athylen und das Nitron 3a. Derartige Nitrone konnen auch durch Addition von N-Athyl-bzw. NMethyl-hydroxylamin an Acetylendicarbonester erhalten werden, so dal3 sich ein sehr einfacher Zugang zu carbonylkonjugierten Nitronen ergibt. Da Cycloadditionen rnit Nitronen sehr gut studiert sind2-6), planten wir, die bci diesen Reaktionen gewonnenen Nitrone zusatzlich durch ihre entsprechenden Cycloadditionsprodukte zu charakterisieren.Beim Erhitzen des Nitrons 3b rnit Acetylendicarbonester in Benzol erhielt man zwar eine Verbindung der gewunschten Summenformel, aber NMR-, IR-, UV-und Massenspektrum7) schliel3en die Struktur 2 fur das Addukt eindeutig aus. 2548,2559, 2568 (1968). (1968).
Excitation (2537 A = 112 kcaljmole) of dimethyl sulphoxide (DMSO) in solution Ieads to singlet excited DMSO (E 8 = 105 kcal/mole) that undergoes three primary reactions: fragmentation to methyl and methanesulphinyl radicals, a bimolecular disproportionation reaction to dimethyl sulphone and dimethyl sulphide by a reaction with a ground state DMSO molecule at higher DMSO concentrations, and deactivation to DMSO ground state molecules.The triplet state of DMSO (ET = 83 ± 3 kcaljmole), if formed at all, appears tobe chemically inert. At relatively dilute DMSO solutions, the fragmentation (Dc~s = 53 kcal/mole) occurs with a quantum yield of0.14 which is independent of the nature of the solvent (acetonitrile, alcohols, water), of the viscosity of the solvents as well as of the pH of the solvents. No H/D and 16 0/ 18 0 exchanges take place thermally or photochemically under the reaction conditions applied.In acetonitrile, the radicais formed in the primary reactions abstract hydrogen atoms from the solvent; in water, electron transfer from methanesulphinyl radical to methyl radical proceeds thereby producing solvated ions, whereas both these reactions occur in alcohols depending upon the alcohols' ability to stabilize such ions. Methanesulphinyl radicals are able to undergo various reactions: they abstracthydrogen from acetonitrile and alcohols, they dimerize in neat DMSO, they transfer an electron to methyl radicals in water, and they add to an aromatic system such as benzene. Methyl radicals, however, were found to undergo exclusively hydrogen abstraction except in water where they accept an electron from the methanesulphinyl radical. DMSO proved itself as a very poor hydrogen donor. Only during photolysis of neat DMSO was the appearance of'dimsyl' radicals, CH 3 SOCH 2 , apparent; their major reaction under these conditions is fragmentation to formaldehyde and methanesulphenyl radicals. A qualitative as weil as a quantitative analysis of all the products formed in neat DMSO and in various solvents has been made; the reaction sequences that are assumed to follow the primary processes can quantitatively account for all the products observed such as methane, methanesulphonic acid, dimethyl disulphide, dimethyl sulphide, and methyl methanethiolsulphonate.Photolysis of DMSO can be sensitized by benzene and toluene whereas p-cymene, tetralin, mesitylene, acetone, and benzophenone are incapable of doing so. Fluorescence quenching of benzene by DMSO and the inefficiency of cyclohexene to quench the benzene-sensitized photolysis of DMSO show that singlet-singlet energy transfer and decomposition of the singlet excited DMSO take place. The kinetics of the methane formation (methanesulphinyl t Present address:
Die durch Cycloaddition von Nitronen a n Acetylendicarbonester oder Propiolester darstellbaren lsoxazolderivate vom Typ 2 konnen auf zwei verschiedenen Wegen, namlich uber einen Hetero-Cope-ProzeB sowie uber den Aziridin-Weg3.4) in Pyrrolderivate iibergehen.Additions to the Triple Bond, XV Rearrangements of Isoxazole Derivatives Isoxazole derivatives of' the general structure 2, which are formed by cycloaddition of nitrones to acetylendicarboxylate or propiolate, can rearrange to the corresponding pyrroles either via a Hetero-Cope procebs or via the aziridine-pathway3,4).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.