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Title: Addition reactions of some unsaturated systems possessing one or more hetero atoms
Author: Foxton, M. W.
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 1965
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The introduction reviews the Michael addition, and shows how the addition of dimethyl acetylenedicarboxylate to heterocycles can be explained if initial attack gives a zwitterion, = +N-Co = Co, which can then react further in several ways. A summary of how the acetylenic ester combines with various heterocycles is given, and brief mention is made of the related Diels-Alder and 1, 3-dipolar additions. Chapter One discusses the reaction of 2-phenylpyridine with dimethyl acetylenedicarboxylate. The initial product has structure [1], which,on heating above its melting point, isomerises to [2], these structures being assigned by consideration of the spectral properties. Heating [1] with excess acetylenic ester gives the 9a-vinyl-9aH-quinolizine, [3], whose spectra resemble those of [1] rather than those of [2]. The 9a-vinyl- 9aH-quinolizines, [4] and [5], are obtained from the acetylenic ester and 2-vinyl- and 2-methyl-6-vinylpyridine, respectively. A minor product from 2-vinylpyridine is [6], and a possible mode of formation is proposed. In Chapter Two, the addition of dimethyl acetylenedicarboxylate to azoles is discussed. Thiazole and 4-methylthiazole give the adducts [7] and [8], while a minor product of the thiazole reaction is [9]. Objections to alternative structures1 for [7] and some analogues are put forward. Benzoxazole forms the adduct [10] which can be reduced to the dihydroderivative [ll]. 2-Methylbenzoxazole and the acetylenic ester give the compound [12], a possible reaction scheme being postulated, and the similar compounds [13] and [14] are obtained from l-alkyl-2-methyl-benziminazoles. The nuclear magnetic resonance spectra of these adducts are discussed, and compared with those of [15] and [16], previously prepared.2 1, 2-Dimethylbenziminazole gives a second adduct which has been shown to be [l7]. The sole adduct from 2-ethyl-1-methylbenziminazole and the acetylenic ester is the analogous compound [18]. Comparison of the nuclear magnetic resonance and ultraviolet absorption spectra of these compounds with those of a minor product from the reaction of 1-methylbenziminazole and dimethyl acetylenedicarboxylate, indicate it has the structure [19], but the major product of the reaction is [20]. A similar compound [21] is obtained from benziminazole. Attempts to convert [19] into [20], or both into the same perchlorate, were unsuccessful. Two adducts [22] and [23] are obtained from 1-methylpyrazole, while 1-methylindazole and the acetylenic ester give [24]. These structures are based mainly on spectral evidence. 1-Methyl- and 1-benzylbenzotriazole react with dimethyl acetylene-dicarboxylate to give 1:2 molar adducts, which are formulated as [25] and [26], on the basis of their reduction and oxidation products, and their respective spectra. Structure [25] is preferred to [27], which might be expected by analogy with earlier results, because of its ready loss of CH2, characteristic of vinyl ethers. A method of formation of [25] and related compounds is suggested. l-Methyl-l,2,4-triazole and the acetylenic ester form the compound [28], but the N-methyl derivative of 3-methyl-l,2,4-triazole gives three 1:2 molar adducts, for which no definite structures could be proposed. The reactions between some diazines and dimethyl acetylenedicarboxylate are considered in Chapter Three. In acetonitrile, the sole products from 2-methyl- and 2,6-dimethylpyrazine and the ester are [29] and [3O], while the similar compounds [31], [32], and [33] are minor products when pyridazine, 3-methylpyridazine, and 1-methylphthalazine are used. The structures [31] and [32], previously described , are confirmed by nuclear magnetic resonance spectroscopy, which was also used to assign structures to the major products of the reactions of the acetylenic ester with pyridazine and its 3-methyl derivative, [34] and [35] respectively. [36], the analogue of [35] is obtained from 3,6-dimethylpyridazine and the ester, but the major product of this reaction is [37], identified by its proton resonance spectrum, which is similar to those of the compounds [12]-[16]. Unlike 3-methylpyridazine, 1-methylphthalazine gives a 1:2 molar adduct with a hydrogen at the bridgehead, [38], and this is isomerised to [39] in acid solution. In aprotic solvents, phthalazine, quinazoline, and quinoxaline give no crystalline products with dimethyl acetylenedicarboxylate, but, in methanol, phthalazine gives [40]. Phenazine and the acetylenic ester in methanol form the adduct [4l], the structure being supported by the proton resonance spectrum, consistent with a symmetrical molecule, and derivatives obtained on reduction and bromination. Chapter four is concerned with alkylquinoxalines and methyl- substituted diazines, whose methyl groups take part in the reactions with acetylenic esters. Thus, 2-methylquinoxaline and dimethyl acetylene dicarboxylate give two isomeric 1:2 molar adducts, [42] and [43]. These structures are based partly on analogy with the "red adduct" from quinaldine4 , and partly on the chemistry and spectra of the compounds. The nuclear magnetic resonance spectrum of [42] is discussed in detail, and a theoretical spectrum of the CH2-CH system has been calculated5, excellent agreement being found between calculated and observed spectra for both methyl and ethyl esters. Reduction of [42] gives [45], and again agreement between observed and calculated proton resonance spectra is found. 2,3~Dimethylquinoxaline forms the methyl analogue of [43] i.e. [44], and the differences in the CH2-CHCOOMe systems of [42] and [44] are used to justify the differences in the respective proton resonance spectra. Attempts to degrade these adducts were unsuccessful. Reduction of [44] gives the 5,6-dihydro derivative, while bromination of [42] gives the 2,3-dibromo derivative, and bromination of [44] gives bromo-compounds, substituted in the benzene ring and/or the methyl side chain. An interesting reaction is the conversion of [44] to [43] by selenium dioxide. Possible ways in which these adducts could be formed are discussed. 4,6-Dimethyl- and 2,4,6-trimethylpyrimidine and 4-methylquinazoline form 1:2 molar adducts with dimethyl acetylenedicarboxylate, whose nuclear magnetic resonance spectra show the presence of CH2-CH groupings. Structures [46], [47], and [48] are proposed for these compounds, although, the CH2-CH systems may be reversed. A 1:3 molar adduct from 2,4-dimethyl-quinazoline and the acetylenic ester is formulated as [49], on the basis of its nuclear magnetic resonance spectrum. 2,3,5,6-Tetramethylpyrazine and the acetylenic ester give a compound, whose structure is considered to be [50], although alternatives are discussed. The similar compound [51] is obtained in small yield from 2,3-dimethylquinoxaline, while 2,5-dimethylpyrazine and dimethyl acetylene-dioarboxylate give an adduct, whose properties support the structure [52]. A scheme is suggested for the formation of this compound. In Chapter Five, adducts from the acetylenic ester and some heterocyoles containing a free amino group are shown to be one of two types. 4-Methyliminazole and indazole form adducts like [53], while indazole, 3-methylindazole, 1,2,3-triazole, benzotriazole, 1,2,4-triazole, and 3-methyl-1,2,4-triazole give adducts of the type [54]. The position of attachment of the side chain cannot be decided, except in the adducts of indazole and 3-methylindazole, [55] and [56] respectively. Unlike the other succinates, [55] and [56] show two sets of peaks in their nuclear magnetic resonance spectra, indicating the asymmetry of the molecules. Diazoaminobenzene and dimethyl acetylenedicarboxylate give three adducts, two of which correspond to [53] and [54], while the structure [57] is suggested for the third adduct.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available