Cyclocondensation reaction

In 2005, Bosch s group developed highly enantioselective DKR processes on the basis of cyclocondensation reactions of chiral aminoalcohols with racemic or prochiral -oxoacid derivatives, providing in a single synthetic step the 

Another example for this mechanistic type is the reaction of2-chloroper-fluoro-l-thiocyanato-1-cyclohexene with gaseous ammonia at room temperature. The 2-amino-4,4,5,5,6,6,7,7-octafluoro-4,5,6,7-tetrahydro-benzothiazole initially formed, subsequently suffers a nucleophilic attack by ammonia and HF elimination to give 2-amino-4,4,5,5,6,6-hexafluoro-7-imino-4,5,6,7-tetrahydro-benzothiazole (91BAU2075). 

Cyclocondensation Reactions of 1,4-Dinucleophilic with Fluoro-containing 1,1-Dieiectrophilic Building Blocks 

4-dinucleophilic building blocks used most are 1,2-disubstituted ethanes of the type HXCHiCHjYH, semicarbazides, thiosemicarbazides, hydroxamic acid amides, amidrazones, and 1,2-disubstituted aromatic and heteroaromatic compounds. 1,1-Dielectrophilic building blocks preferentially used are perfluorinated carboxylic acids and their derivatives, such as acid halides, anhydrides, imidoesters, nitriles, perfluoroalkyl chlorosul- 

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Cyclocondensation reactions starting from two components are possible only when both of them have two reactive centers An initial electrophilic-nucleophilic interaction yielding a linear product is followed by a second electrophilic-nucleo-... 

Cyclocondensation reactions with perfluoroalkyl-subsbtuted CO and CN multiple bond systems can be divided into several subgroups, according to the charge pattern of both reactants On the basis of this simple concept, hetero-l,3-dienes should undergo two types of condensation reactions, classified by the number of skeleton atoms of the diene being incorporated into the ring system (equation 10). 

The 1,5-isomers 13.3 (E = S) are colourless, air-stable solids. They are prepared by the cyclocondensation reaction of R2PN2(SiMe3)3 with sulfur dichloride or thionyl chloride. A similar cyclocondensation process, using a mixture of SeCU and Sc2Cl2 as a source of selenium, produces a mixture of the isomers 13.2 and 13.3 (E = Se, R = Ph). The structures of 13.3 (E = S, R = alkyl, aryl) are folded eight-membered rings with a cross-ring S S distance of ca. 2.50 This structural... 

Many furanones (including furanose carbohydrates) have been used as synthons with 1,2-benzenediamines to afford quinoxaline derivatives. The following examples illustrate the main types of such cyclocondensation reactions. 

As cyclocondensation reactions generally require heating at high temperatures to achieve conversion, such procedures are expected to be well-suited... 

Abstract Controlled microwave heating has foimd many important applications in the synthesis of heterocycles. Almost all kinds of heterocycles have been prepared (or their preparation attempted) with the aid of microwaves. Many examples of cyclocondensations, reactions where two or more fimctional groups combine with the loss of another small molecule (usually water), have been described. Moreover, microwave irradiation successfully induces cycloaddition reactions, especially in the cases where high temperatures are required. This review collects the most representative examples of the application of microwaves to these two kinds of transformations. Except for a few examples, all the reactions selected have been carried out imder controlled microwave irradiation using dedicated instruments. 

Keywords Cycloaddition reactions Cyclocondensation reactions Heterocycles ... 

This cyclocondensation reaction has also been examined with substituted levulinic acids ... 

Tris(trimethylsiloxy)-methoxy hexatriene undergoes with aliphatic imidazolides in the presence of a Lewis acid a 5C -f 1C cyclocondensation reaction leading t° aromatic products 18]... 

Amino-3-(methoxycarbonyl)pyrazine 89 is a versatile reagent for the cyclocondensation reactions leading to heterocondensed pteridines 90-93 (Scheme 6) <2001JHC1173>. 

Following the communcation in 2004, a full report appeared that described type Ilac cyclocondensation reactions between dihydroisoquinolines and a-nitrocinnamates leading to complex fused pyrroles <06JOC9440>. The latter were converted into the lamellarin alkaloids and related analogues. 

The preparation of 2-aminopyrroles was accomplished with type Ilae zinc-catalyzed cyclocondensation reactions between (i-cyanoketones and primary amines <06T1452>. 

An effort to improve the efficiency of the nucleophilic displacement of halogens in a cyclocondensation reaction of primary amines with alkyl dihalides for the synthesis of N-phenylpiperidine through the use of microwave irradiation (80100 W, 120 °C, 20 min, 96% yield) was reported this year <06JOC135>. 

Several 3-mercapto-l,2,4-trizines have been synthesized through the condensation of thiosemicarbazide with diketones under microwave irradiation in a solventless system <06PS87>. The synthesis and cyclocondensation reactions of 3-substituted-5-(2-aminobenzyl)-l//-[l,2,4]triazin-6-ones have been reported <06JHC613>. 

The cyclizations to obtain cyclic thioureas have been performed using thiocarbonyldiimidazole.232 Reaction of methyl acetoacetate, thiourea and an aliphatic aldehyde in the presence of the zinc iodide (Znl2) was studied. Under the normal pressure, reaction has not been occurred whereas at high pressure (300 MPa) conditions 3,4-dihydropyrimidine-2-thione was obtained only in 10% yield.233 The same one-pot three-component cyclocondensation reaction in the presence of iodide (I2) provides a variety of 3,4-dihydropyrimi-dine-2-thione in high yields.234 Condensation reaction of thioureas with a,p-unsaturated ketones in the presence of the sodium methoxide in methanol affords 3,4-dihydropyrimidine-2-thione derivatives.235,236 Acylation of N,N -disubstituted thioureas with methyl malonyl chloride followed by base-catalysed cyclization leads in the formation of l,3-disubstituted-2-thiobarbituric acids (Scheme 78).237... 

The best preparation of 130 involves the reaction of sulfamide with PC15 followed by a [5+1] cyclocondensation reaction between the /)/,v(phosphazo)sulfone Cl3P=N-S02-N=PCl3 and hexamethyldisilazane. The reactions of 129 and 130 with nucleophilic reagents have been studied in considerable detail, with emphasis on the regiochemistry.285... 

Palladium-catalyzed cyclization reactions with aryl halides have been used to synthesize pyrazole derivatives. V-Aryl-lV-(c>-bromobenzyl)hydrazines 26 participated in a palladium-catalyzed intramolecular amination reaction to give 2-aryl-2W-indazoles 27 . Palladium-catalyzed cascade intermolecular queuing-cyclocondensation reaction of o-iodophenol (28) with dimethylallene and aryl hydrazines provided pyrazolyl chromanones 29 <00TL7129>. A novel one-pot synthesis of 3,5-disubstituted-2-pyrazolines 32 has been achieved with an unexpected coupling-isomerization sequence of haloarene 30, propargyl alcohol 31, and methylhydrazine <00ACIE1253>. 

An alternative route to furyl compounds of similar structure was reported by Yao et al. <2005BML511> the same starting amine 409 was N-aminated to the 1,2-diaminopyrazinium mesylate 412, which was ring-closed by treatment with furylaldehyde to yield 413 in rather poor yield. The synthesis of the pyrrolidinylcarbonyl derivative 415 in a cyclocondensation reaction of 414 by use of polyphosphoric acid was reported by Giardina et al. <1995FA405>. 

Apart from some special cases, the ring-closure step in the course of the synthetic pathway is often condensation reaction and, thus, these transformations can be considered as cyclocondensations . Reactions following a few other mechanisms like cycloaddition, electrocyclization, and intramolecular nucleophilic addition of electron pair of an atom to a multiple bond also occur relatively often. Because of the fairly large complexity of the ring systems belonging to this chapter, the treatment according to the heteroatomic combinations seemed the most straightforward. Thus, the fused... 

Both amino groups of 3,5-diamino-4-phenylpyrazole reacted with EMME during 2 min. at reflux [83JCS(P1)11], The amino group at position 3 underwent a cyclocondensation reaction to form the bicyclic pyraz-olo[l,5-a]pyrimidine, while the amino group at position 5 participated in an addition reaction to give a (2,2-diethoxycarbonyl-l-ethoxyethyl)amino side-chain. Pyrazolo[l,5-a]pyridine (25) was obtained in 27% yield. 

For highly functionalised dienes and their equivalents, also very useful for designing organic syntheses involving cycloaddition and cyclocondensation reactions, see S. Danishefsky, CHEMTRACTS Organic Chemistry, 1989, 2, 273-297. 

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