Enaminoketones, condensation with

Two closely related reports of pyrazole generation by condensation of substituted hydrazines with enamino carbonyl compounds have appeared. In situ formation of an enaminoketone, by treatment of a diketone with dimethylformamide dimethyl acetal, was followed by tandem Michael addition-elimination/cyclodehydration under aqueous conditions in sealed microwave vessels (Scheme 3.12)17. Isoxazoles and pyrimidines were also prepared by replacing the substituted hydrazine with hydroxylamine or amidines, respectively (see Chapter 5, Section 5.3.2). The overall process may be regarded as another example of a multi-component coupling. In a similar fashion, enamino propenoates were condensed with substituted hydrazines to afford substituted pyrazoles (see Chapter 5, Section 5.3.2) (Scheme 3.12)18. 

The reaction sequence of Scheme 3 might well be classified as an imidazole synthesis from other heterocycles, but it seems more logical to treat this as a cyclization involving formation of the 1,5-bond. The enaminoketone condensation products (12) of 3-amino-l,2,4-oxadiazoles and 1,3-dicarbonyl compounds are cyclized by base to imidazoles (13) in 60-80% yields." Such a reaction makes use of the well-established general attack of a nucleophilic center in the side chain on N-2 of the oxadiazole ring. Benzamidine combines with 2-amino-3-phenacyl-l,3,4-oxadiazolium bromides to produce 1-acyl-amino-2-benzimidoylamino-4-arylimidazoles. ... 

A related amination/rearrangement/cyclization tandem sequence had been introduced by Cossy [49]. Starting from cyclic epoxyketones 224 the reaction with propargylamines 225 caused an oxirane-opening condensation process to generate the enaminoketones 226. Upon heating in toluene to reflux, aza-Claisen rearrangement delivered the intermediate allenyl imines 227, which... 

Condensation reactions of enaminoesters, enaminoketones, and enam-inonitriles with benzo- and chloronaphthoquinones have been described (94JIC281). Utilization of diamines (38) as novel synthons in the Nenitzescu reaction has resulted in a new synthesis of 2-(3-benzofuryl)indoles (40) [95KFZ(9)47,95MC69].The pathway in the scheme leading to 40 has... 

The microwave-mediated condensation of hydroxylamine with enaminoketones to generate isoxazoles has been mentioned earlier (refer to Scheme 3.12)17. In a procedure analogous to the Paal-Knorr thiophene synthesis, 2-aminoacyl carbonyl compounds... 

The reaction between thioacylformamidines and ketenes leads to thiazine-6-ones (29) (Scheme 16) (75T3055). 4-Amino-4//-thiazines (30) are obtained by condensation of thioacylformamidines with acetylenic compounds (Scheme 17) (85JOC1545). Thiobenzoyl-1 and )V,A/-diethylami-nothiocarbonyl isocyanates and isothiocyanates have been reacted with enaminoketones and ynamines. Enaminoketones and ynamines reacted with thiobenzoyl isocyanate give thiazine-4-ones 31 and 32, respectively (Scheme 18) (76BCJ2828 85ZC324). 

Pyrazolooxazepine 153 was synthesized starting from the condensation of hydrazinol 151 with enaminoketone 150. When the isolated ester intermediate 152 (R = OMe) was saponified, ester hydrolysis afforded acid 152 (R = H), which cyclized on subsequent treatment with l-ethyl-3-[3-(dimethylamino)propyl] carbodiimide hydrochloride (EDC) and 1-hydroxybenzotriazole (HOBt) to form oxazepine 153 (Scheme 22) <2003TL5867>. 

Synthesis of annelated diazepines based on unsaturated aromatic diazepines may involve the preliminary transformation of ketones into the corresponding l,3-diaryl-2,3-dibromopropane-3-ones (chalcone dibromides). The interaction between o-PDA or some of its substituted analogues with chalcone dibromides leads to the formation of aziridine derivatives [64] (see Chap. 1). However, in the case of 4-nitro-o-PDA, either azirenoquinoxalynes 53 or benzodiazepine derivatives 54 may be obtained depending on the reaction conditions [65] (Scheme 4.15). Diazepine derivatives 56 are obtained by the condensation of chalcone dibromides 51 with 5,6-diamino-1,3-dimethyluracil 55 [66], but aziridine derivatives are not isolated in this reaction. It should be noted that compounds 54 and 56 are formed owing to cyclization of the intermediate (3-enaminoketones [65, 66, 67] and are easily isolated from the reaction mixture. 

Condensation of 2,2-dimethoxy-l-methyl pyrrolidine(piperidine) with 1-indanone, 1-tetralone, 4-thiochromanone, butyrolactone, phthalide and substituted 2-oxindoles gives the corresponding enaminoketones. ... 

Unsymmetrical 1,4-dihydropyridines can be produced by conducting the Hantzsch synthesis in two stages, i.e. by making the (presumed) aldol condensation product separately, then reacting with ammonia and a different 1,3-dicarbonyl component, or an enaminoketone, in a second step. ... 

Condensation of o-aminophenylacetaldehyde dimethylacetyl with /S-diketones followed by treatment of the intermediate enaminoketones with acetic acid affords l/f-benz(f>]azepine in high yields <93BSF143>. Cyclization of the allene (142 R = —CH CHj) by heating in toluene affords the azepines (143 R = —CH=CH2) and (144) in a stereoselective manner (Equation (13)). Where,... 

The condensation of enaminoketones derived from acetophenones with 1,4-naphthoquinone resulted in the furan-fused (3-benzoylnaphtho[l,2-l ] furan-5-ol) (14T9352). 

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