Structural characterization of new 2-aryl-5-phenyl-1,3,4-oxadiazin-6-ones and their N-aroylhydrazone precursors (original) (raw)
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Electrocyclic ring opening reaction of a 1,3,4-oxadiazin-6-one into its azaketene tautomer
Tetrahedron Letters, 1984
5-Methyl-Z-phenyl-1,3,4-oxadiazin-6-one undergoes cycloaddition with 2methylpropenylpyrrolidine. One of the cycloadducts is derived from the Diels-Alder reaction of a transient azaketene tautomer. In recent years the Diels-Alder reaction of simple heterosubstituted 1,3-dienes has emerged as a powerful method for preparing highly functionalized ring systems.' Dienes substituted with two different heteroatoms are of considerable interest because of their value in natural product synthesis. 2-6 The synthetic utility of the inverse electron demand Diels-Alder reactions of heteroaromatic systems, however, has not been explored in great detail.' This is primarily due to the ambiguities concerning the mode of cycloaddition and the lack of demonstrated or dependable synthetic procedures and applications. The 2,3_diazabutadiene unit is incorporated in the 1,3-H d shift 5489
The latest advances in chemistry of 1,2,4-oxadiazines (microreview)
Chemistry of Heterocyclic Compounds, 2017
Fedor Ivanovich Zubkov was born in 1973 in Moscow, Russia. He earned a Master's degree in chemistry at the People's Friendship University of Russia in 1996, followed by a PhD in chemistry in 2000. From 2001 until the present time he works as a docent at the Organic chemistry department of People's Friendship University of Russia. His scientific interests include nitrogen heterocycles, furan, and cycloaddition reactions. Anton Andreevich Shetnev was born in 1985 in Yaroslavl, Russia. He graduated from the Yaroslavl State Technical University in 2007 with specialization in chemistry, followed by a PhD in chemistry in 2011. Currently he works at the Organic chemistry department of People's Friendship University of Russia. His scientific interests include medicinal and process chemistry, nitrogen-containing heterocycles, and reactions of amidoximes. for converting these compounds to 1,3-oxazoles, 7 4-hydroxypyrimidines, 8 1,2,4-oxadiazoles, 9 and N-hydroxyimidazoles 10 continue to attract the interest of researchers to oxadiazines as synthons for organic chemistry. Since publication of the latest review on chemistry of 1,2,4-oxadiazines in 2011, 11 a significant number of new interesting reports have appeared in this field, thus we consider it necessary to compile a systematic review of the most recent data.
Tetrahedron, 1998
5(4/-/)-Oxazoiones I andmtinchnones 3 arereactedwith a'iphenylvmylphcephonium bromide 2a In give, ~aough a cycload&fion reaction, pyrrole dexivatives 4a-d and 7a-c uusubstitmed at C-3 and C-4. The use of mbstltuted vinyiphosphonium salts 2b,e anddipohis I and 3 allows the isolation of 3methylpyrroles 4e,f and 7d,e and 3-pyrrolecarboxylic acids 9a-e, respectively. The cydoaddition reactions proceed with high regioselectivity because of the positive interaction of phosphonium group of 2 and carbonyl group of dipoles I and 3. © 1998 Published by Elsevier Science Ltd. All rights reserved. 5(4/-/)-Oxazolones 1 are very interesting synthons for the preparation of many different nitrogen containing heterocycles. 2a An important feature of these substrates is their different reactivity toward a same class of reagents depending on the reaction conditions. Thus, it is possible to synthesize different heterocyclic compounds as deduced in previous papers. 3-6 The basic conditions allow the generation of a carbanion on C-4 which can undergo a great number of reactions (alkylation, Michael addition to electron poor double bonds), while neutral conditions enhance the reactivity of oxazolones as 1,3-dipolax reactants (azomethine ylides). In a previous paper 7 we reported the reaction of 5(4/-/)-oxazolones I with tfiphenylvinylphosphonium bromide 2a, an electron-poor olefin, in order to obtain Al-pyrroline-2-carboxylic acid derivatives. The first step of this synthesis is the addition of carbanion on C-4 of oxazolone, generated in basic conditions, to the vinyl group of compound 2a. As reported in the literature, the vinyl phosphonium salt 2a is also a good dipolarophile which can react with diazo derivatives s-10 and azomethine ylides 11-12 generated from azirines by photochemical reaction.
Journal of Molecular Structure: THEOCHEM, 1998
AM1 semiempirical and B3LYP/6-31G(d)/AM1 DFT computational studies were performed with the aim to determine which 1,3,4-oxadiazoles would participate in Diels-Alder reactions as a diene and under which conditions. Variously substituted 1,3,4-oxadiazoles were selected for this study. Their reactivity was compared with cyclopentadiene since it is a traditional diene for the Diels-Alder reaction. The reactivity was evaluated through the frontier molecular orbital (FMO) energy gap between the pair of reactants, the energy changes in the FMO necessary to bring reactants to the transition state, and through activation barriers for cycloaddition. The stability of the cycloadduct was investigated and in some cases, a second addition of a dienophile was explored. The results were compared with experimental observations, and in this way, the reliability of the chosen computational approach was tested. All of our computational conclusions were in agreement with experimental observations for the reactivity of 1,3,4-oxadiazoles.
Tetrahedron Letters, 2002
Substituted bicyclo[5.3.0]azulene compounds are synthesized by intermolecular [8+2] cycloaddition reactions of lactone 1 with vinyl ethers-acetal decomposition products-are described. The reactions were found to be temperature and solvent dependent. Azulene compounds have recently attracted attention due to their specific physical and chemical properties. 1 Depending on the substituents attached to the rings, azulene derivatives have a range of color spectra from red, blue, purple to green. The aromaticity of the fivemembered ring of azulene has been a subject for several important modifications, namely Friedel-Crafts acylation, Mannich aminomethylation, condensation, Vilsmeier formylation, among others. An azulene ring has been synthesized by cycloaddition reactions of the activated troponoid and the active methylene compound. 2 In addition to the [6+4] addition mode, some of these systems are known to undergo [8+2] cycloaddition. 2 In an effort to synthesize azulene derivatives as chromophores, we were interested in starting with the lactone 1. There are few reports for the synthesis of azulene compounds. 2 However, for the reaction intermediate, conditions had not been clearly defined, resulting in unreproducible results. In this communication, we report an improved procedure toward the synthesis of the [5.3.0] ring system of azulenes (Scheme 1). Upon thermolysis, the acetal 2 was decomposed into the active vinyl ether 4 and methanol. The cycloaddition reaction between the lactone 1 and 4 forms azulene 3 as a single product.