Self-condensation product

HO—R—COOH, or an amino acid, H2N—R—COOH. In some cases, such monomers self-condense to a cycHc stmcture, which is what actually polymerizes. For example, S-caprolactam (1) can be thought of as the self-condensation product of an amino acid. Caprolactam undergoes a ring-opening polymerization to form another... 

Self-condensation products of 4-nitrotoluene-2-sulfonic acid or its derivative 4,4 -dinitto-2,2 -stilbenedisulfonic acid or 4,4 -dinitto-2,2 -dibenzyldisulfonic acid [728-42-7] and products of their treatment with teduciag or oxidizing agents. An example is Direct Yellow 11 (Cl... 

Although chemically related to the above cycloalkylamines, pentethylcyclanone (71) is stated to have antitussive activity. The compound is prepared rather simply by alkylation of the anion (70a) of the self-condensation product of cyclopentanone (70) with N-(2-chloroethyl)-morpholine. ... 

Water, which can be taken to a minimum by the use of molecular sieves, can produce a lactamide either through direct reaction with the aziridinone intermediate, or upon hydrolysis of oxazolidinone self-condensation products, previously obtained also in the presence of a strong non-nucleophilic base (H ) (ref. 17). The recently reported 0-self-alkylation compound H bears the (S,S)-configurations at the unreacted C-Br and newly formed C-0 bonds. The presence of bromine was expedient for the x-ray assessment of configuration at the two chiral centers of 11 which forms in high diastereoisomeric excess (ref. 5). 

Although 2,4-dichloro-6-ethyl-5-fluoropyrimidine (13) contained the correct carbon skeleton for condensation with the acetophenone, only self-condensation products were obtained following metallation with LDA. A reduction in electrophilicity was achieved by removal of the 2-chloro substituent via a three-step sequence involving hydrolysis of the more reactive 4-chloro substituent, followed by hydrogenation of the 2-chlorine and rechlorination with phosphorous oxychloride. The overall yield for the three steps resulting in 4-chloro-6-ethyl-5-fluoropyrimidine (14) was 72%. 

Under carefully worked out reaction conditions, 2b can give the 3-bromo compound 94 (CHC13,0-5°C) or the 3,3-dibromo compound 95 (2M NaOH, 0-5°C). The reactions of 94 and 95 with N-nucleophiles proceed differently. Refluxing 94 in ethanol gives dimer 96, which is clearly distinct in structure and properties from other self-condensation products of tetramic acid (85AJC1847). Otherwise, 95 and yV-methyl-A-phenylhydrazine under refluxing in ethanol form 3-hydrazone 92a in 60% yield (90TH1). (See Fig. 42.)... 

In 1979, Ferles and Silhankva showed that ethyl nicotinate was converted into the self condensation product 4-(2-carboethoxypyridyl)-3-... 

In spite of the successful implementation of the concept of remote activation of an anomeric 2-pyridylthio group, there emerged various issues and questions. The absence of self-condensation products could be ascribed to the use of excess acceptor in all cases, and possibly to the coordination of the mercuric salt to the free hydroxy groups of the donor, thereby diminishing their reactivity. However, the necessity to use an excess of acceptor (> 5 eq), the formation of anomeric mixtures of glycosides, and the use of a mercuric salt, limited the generality of this method of glycoside synthesis. 

Selenophenes (195) have been obtained by the condensation of phenacyl bromides with /S-aminovinyl selenoketones, readily obtained from chloroimmonium salts (194) (76S521). The reaction of o-methylselenobenzaldehyde with chloroacetone gives directly an excellent yield of 2-acetylbenzo[6]selenophene (196) (72BSF1643). However, the reaction with bromoacetic acid yields not only the corresponding 2-carboxylic acid (197), but also the self-condensation product (198). 

Hydroxymethylation of guaiacyl acetone (VII) yielded an amorphous solid, probably a self-condensation product after being methylolated in several positions. Veratyl acetone (VIII) gave a crystalline product in good yield which had no CO group. It can be assumed that the CO group was reduced by a crossed Cannizzaro reaction, and a dimeric product was formed, whose structure is not known yet. 

A -Piperideine (17) has been shown to be a precursor of quinolizidine alkaloids in whole plants (cf. Vol. 8, p. 3). However, neither it nor its self-condensation products could be detected as products in the enzymic reaction. [This conclusion is not completely unambiguous, albeit reasonably safe, because the products of the reaction of diamine oxidase, the first of which is (17), were simply compared with those of the alkaloid synthase reaction by g.l.c., and the products of the two reactions were found to be different].11 It seems likely at this stage that (17) is not normally implicated in quinolizidine biosynthesis but can be substituted for an enzyme-generated intermediate via its open form (32) (see Scheme 5). Since no intermediates earlier than (27) could be detected, it is suggested that biosynthesis in vitro and in vivo proceeds by a series of enzyme-linked intermediates (see Scheme 5), none of which is desorbed from the enzyme or enzyme-complex until (27) is liberated. However, in some plants, biosynthesis must stop with the liberation of a compound (31), having the lupinine skeleton... 

Diketopiperazines (the bimolecular self-condensation products of a-amino acids) also react with phosphoryl and phosphorus halides to give halopyrazines. Treatment of 2,5-diketo-3,6-dimethylpiperazine with phosphoryl chloride yields a mixture of 2-chloro- and 2,5-dichloro-3,6-dimethylpyrazines the monochloro compound is the predominant product [Eq. (14a)].134,135 Trichloropyrazine has been isolated from the reaction of triketopiperazine with phosphoryl chloride or phosphorus pentachloride [Eq. (15)].273... 

Another field of research is concerned with the one-pot synthesis of this system from readily available starting materials. In Scheme 12, reaction of phenyl azide and malononitrile in the presence of sodium ethoxide leads, via the intermediate triazole (139), to the self-condensation product (140), itself a triazolopyrimidine. In the presence of other nitriles the preferred formation of the more useful compounds (141) occurs in low to moderate yields with small amounts of dimer <87JHC997>. Direct synthesis of the 5,7-dione derivatives (143) (60-90%) is achieved by the reaction of the readily available aminopyrimidinedione (142) with an azide iminium salt in dichloromethane at moderately high dilution <87JHC1493>. 

Four products result from the aldol condensation of acetone and acetophenone. The two upper compounds are mixed aldol products, and the bottom two are self-condensation products. 

As in (b), a mixture of products is formed because both carbonyl partners contain a-hydrogen atoms. The upper two products result from mixed aldol condensations the lower two are self-condensation products. 

Chlorophthalazine is quite reactive to many basic nucleophiles but reacts sluggishly with aqueous or alcoholic alkali. In contrast, it is very rapi y hydrolyzed by warm, concentrated hydrochloric acid as are its diazine isomers. In hydrolysis with very dilute acid or with water, it forms some phthalazinone but mostly the self-condensation product which hydrolyses to give 2-(r-phthalazinyl)-phthalazin-l-one (70% yield). Such self-condensations in diazanaph-thalenes and in monocyclic azines are always acid-catalyzed (Sections II, C and III,B). With methanolic methoxide, 1-chlorophthalazine (65°, few mins), its 7-methoxy analog (20°), and 1,6- and 1,7-dichlorophthalazines (20°) readily undergo mono-substitution. 

The structure of the self-condensation product of 3-chloro-6-methylpyridazine has been now proved on the basis of chemical and spectroscopic evidence to be correct, as suggested previously as 67. 

Synthesis of giycidic esters. The Darzcas reaction fails with compounds such as acetaldehyde which give only self-condensation products. Borch has described a new procedure which is generally applicable. The a-bromo ester anion (2) is smoothly generated by reaction with lithium bis(trimethylsilyl)amide in THF at —78". Addition of the aldehyde or ketone at — 78° followed by workup aflbrds the corresponding... 

The method first described by Conant (1580) for preparing hexamethyl-2,5-dihydropyrazine from 3-methylbutanone with warm aqueous alkaline potassium ferricyanide has been expanded into a simple one-step selective way of preparing a-amino-a,Q -dialkyl ketones and/or their self-condensation products, hexaalkyl-... 

Product A is from the enolate of the more substituted side just the self-condensation product from the aldehyde, of the ketone reacting with the aldehyde, and product B is... 

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