Transmission d'un effet stérique péri à travers un noyau hétéroaromatique—II

Maury, Georges; Pigiere, Ch.

doi:10.1016/s0040-4020(01)97720-8

Cited by 4 publications

(3 citation statements)

References 13 publications

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“…In our opinion the relatively high yields of compounds 14 and 15 and the fact that the products 18 and 19 are formed indicate that the mechanism of cyclization in these cases includes a stage with the formation of ylides of type 8 from salts with structure 20 ((E)-isomers) (Scheme 2). It should be noted that the 1,8-dimethyl-1H-imidazo[1,2-a]pyridin-4-ium salt in the form of the iodide was described earlier [12,13], but its method of synthesis involved alkylation of the corresponding 8-methylimidazo[1,2-a]pyridine. Thus, we have found a new method for the production of derivatives of the azolo[a]pyridine system alkyl-substituted in the pyridine part of the molecule by annelation of the four-carbon fragment to the azole.…”

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confidence: 99%

Synthesis of azolo[a]pyridines from 5-(bromomethyl)hept-4-en-3-one and 5-bromopent-3-en-2-one derivatives

Потиха

Turelik

Ковтуненко

2012

Chem Heterocycl Comp

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Keywords: 5-(bromomethyl)hept-4-en-3-one, 5-bromopent-3-en-2-one, imidazo[1,2-a]pyridine, pyrido-[1,2-a]benzimidazole, thiazolo[3,2-a]pyridine, [1,2,4]triazolo [4,3-a]pyridine.γ-Halo-substituted unsaturated ketones are highly reactive compounds and are the synthetic equivalents of 1,4-dielectrophilic synthons. On account of their relatively poor availability they were used predominantly for the production of pyrroles in reactions with primary amines [1][2][3][4][5]. We recently found convenient methods for the synthesis of the azolo[a]pyridine system derivatives on the basis of (2Z)-4-bromo-1,3-diphenyl-2-buten-1-one (γ-bromodypnone) and its derivatives [6][7][8]. While continuing investigations in this direction we turned to γ-halo ketones of the aliphatic series.The structural features of (4Z)-5-(bromomethyl)-2,2,6,6-tetramethylhept-4-en-3-one (1) make it possible to regard it as an analog of γ-bromodypnone; there are nonenolizing groups at the carbonyl group and at the C=C double bond, and their volume leads to configurational stability for the molecule in the form of the (Z)-isomer [9]. Properties of this compound have hardly been studied at all, and only the formation of a quaternary triphenylphosphonium salt [9] and intramolecular cyclization to 2,4-di-tert-butylfuran [10] are known.We have established that compound 1, like γ-bromodypnone, forms quaternary azolium salts 2 with high yields when a mixture of the bromo ketone 1 and azole is kept in benzene at room temperature for several days (Scheme 1), as described in [7,8] (Table 1). Difficulties in the isolation of the alkylation products 2b,e in pure form only arose in the case of reactions with 1-benzyl-1H-imidazole and 1-methyl-1H-1,2,4-triazole. When the reaction is conducted under standard conditions (benzene, 25°, 2-3 days) the reaction mixture still contains the initial azole as impurity (15-20%), which subsequently initiates cyclization of the salts 2b,e during

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confidence: 99%

Synthesis of azolo[a]pyridines from 5-(bromomethyl)hept-4-en-3-one and 5-bromopent-3-en-2-one derivatives

Потиха

Turelik

Ковтуненко

2012

Chem Heterocycl Comp

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“…Ph [21,70,71] The influence of some substituents has also been studied; [70] among the alkyl substituents, the 7-methyl group was found to exert the strongest activating effect. These experimental findings have also been supported by theoretical calculations.…”

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“…Scheme 18 Quaternization of Imidazo[1,2-a]pyridine [21,70,71] As most ring-closure methods as well as the further transformations of the substituents are analogous to those discussed in the previous subsection (i.e., with the basic ring system 1, Product Subclass 12.5.1), this chemistry will be treated more concisely and references will be given to the analogous section describing the particular chemical transformation of the derivatives of 1. Those reactions will be emphasized which are specific for these fused imidazodi-or polyazines.…”

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Product Class 5: Azaindolizines with Two Nitrogen Atoms in the Five-Membered Ring

Neier¹,

Bellus²

2002

Category 2, Hetarenes and Related Ring Systems

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In contrast to Section 12.5.1.1.1.1, where in most cases the first reaction step is the quaternization of a pyridin-2-amine derivative followed by nucleophilic attack of the 2-amino group on an appropriate functional group to form the imidazole ring, several ring closures have been elaborated starting from substituted pyridin-2-amines. In these cases, the â-carbon atom of the carbon chain attached to the 2-amino group bears an appropriate functional group, and a nucleophilic attack of the pyridine ring nitrogen atom at this center results in formation of the imidazole ring. Such syntheses are shown in Scheme 8.

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