Hydroxy compounds, condensation

Benazolin may be prepared from 2-amino-4-chlorobenzthiazole, obtained by ring closure from o-chloroaniline and thiourea. 2-Amino-4-chlorobenzthiazole is converted into the 4-chloro-2-hydroxy compound, condensed with ethyl chloroace-tate and hydrolysed to the endproduct. 

Thus the condensation of dichloroether or chloroacetone fails to give the parent compound, 2-hydroxythiazole (158a), Rj = R2 = R3 = H (221). However, 2-hydroxythiazole can be obtained in 12% yield from chloro-acetaldehyde (386). The condensation of ammonium thiocarbamate with cf-chloroketones gives the corresponding 2-hydroxy derivatives in 25 to 70% yields (76, 221, 304, 412) (Table 11-24). These compounds condensed with ClP(S)(OEt)2 give the corresponding 2-thiazolyl-thiophosphates (791). 

Formaldehyde condenses with itself in an aldol-type reaction to yield lower hydroxy aldehydes, hydroxy ketones, and other hydroxy compounds the reaction is autocatalytic and is favored by alkaline conditions. Condensation with various compounds gives methylol (—CH2OH) and methylene (=CH2) derivatives. The former are usually produced under alkaline or neutral conditions, the latter under acidic conditions or in the vapor phase. In the presence of alkahes, aldehydes and ketones containing a-hydrogen atoms undergo aldol reactions with formaldehyde to form mono- and polymethylol derivatives. Acetaldehyde and 4 moles of formaldehyde give pentaerythritol (PE) ... 

Hydroxyisoquinolines. Hydroxy groups in the 5-, 6-, 7-, and 8-position show phenoHc reactions for example, the Bucherer reaction leads to the corresponding anainoisoquinolines. Other typical reactions include the Mannich condensation, azo-coupling reactions, and nitrosation. Both 0-methyl and /V-methyl derivatives are obtained from the methylation of 1-hydroxyisoquinoline, indicating that both tautomeric forms are present. Distillation of various hydroxy compounds, eg, 1- and 4-hydroxyisoquinoline, with zinc dust removes the oxygen. Treatment of 1-isoquinolinol with phosphoms tribromide yields 1-bromoisoquinoline [1532-71 -4] (178). 

This system was slightly modified by R J. Flory, who placed the emphasis on the mechanisms of the polymerisation reactions. He reclassified polymerisations as step reactions or chain reactions corresponding approximately to condensation or addition in Carother s scheme, but not completely. A notable exception occurs with the synthesis of polyurethanes, which are formed by reaction of isocyanates with hydroxy compounds and follow step kinetics, but without the elimination of a small molecule from the respective units (Reaction 1.3). 

The condensation of aromatic aldehydes with anhydrides is called the Perkin reaction When the anhydride has two a hydrogens (as shown), dehydration always occurs the P-hydroxy acid salt is never isolated. In some cases, anhydrides of the form (R2CHC0)20 have been used, and then the hydroxy compound is the product since dehydration cannot take place. The base in the Perkin reaction is nearly always the salt of the acid corresponding to the anhydride. Although the Na and K salts have been most frequently used, higher yields and shorter reaction times have been reported for the Cs salt. Besides aromatic aldehydes, their vinylogs ArCH=CHCHO also give the reaction. Otherwise, the reaction is not suitable for aliphatic aldehydes. ... 

In the condensation of diols, halogenated alcohols, amino alcohols, cyclic hydroxy ethers, or other bifunctional hydroxy compounds with carbodiimides, 5-, 6-, and 7-membered 1,3-O-N- or l,3-7V,7V-heterocyclics are obtained [14]. 

Little information is available upon hydrogen bond reactions in vapour phase adsorption, except in the important reactions of proteins and textile fibres with moisture, which have received widespread study. In these reactions substrate-water hydrogen bonds are undoubtedly responsible for the initial monolayer adsorption of water with increase in vapour pressure the adsorbed water condenses into multilayers by formation of water-water hydrogen bonds. Adsorption of organiq molecules of low molecular weight, in the vapour phase, on nylon or wool is considerably greater when they contain a hydroxylic group than when they do not [8] (Table 5), so that the hydroxy-compounds... 

In several cases, the intermediate hydroxy compound may be formed in an undetectable amount so that the reaction appears as a direct formation of a,(3-unsaturated carbonyl compound by condensation of two carbonyl compounds... 

Aldol condensation with aldehydes and ketones gives hydroxy compounds (265 — 267) which usually spontaneously lose water (by a reverse Michael addition) to give unsaturated compounds (268). 

In the 1,4-benzoxathiane series, neither dehydration of the hydroxy compound (189) nor elimination of ethanol from (190) give very satisfactory yields of (184) and once again the best yield (76%) is obtained by pyrolysis of the 2-acetoxy derivative (191). 3-MethyI-l,4-benzoxathiin is obtained by an analogous route, but 2,3-diphenyl-l,4-benzoxathiin is conveniently prepared by a one-step condensation of 2-mercaptophenol and benzoin in 21% yield <66HC(21-2)852>. 

They have also been synthesised by condensing salicylic acid with phenols through the agency of sulphuric acid, acetic anhydride, etc. (B., 21, 502 24, 3982 25, 1652 26, 71 27, 1989 A., 254, 265). All four possible mono-hydroxyxanthones have been prepared in this way, as have some of the poly-hydroxy compounds. These latter are the more important. 

Benzo[6]thiophene aldehydes have been condensed with a variety of active methylene compounds, including cyclic511, 644 and open-chain645-647 ketones, aliphatic aldehydes,90 benzyl cyanides,93-436 malononitrile,487 rhodanine,144,648 hippuric acid,477 barbituric acid,487 diethyl malonate,487 and malonic acid (Section VI,M). Aliphatic nitro compounds condense smoothly with most benzo[6]-thiophene aldehydes03,141,337,343, 556,640,650 (except 5-hydroxy- and... 

We wish to report a new approach to condensation reactions of hydroxy compounds related to the Ritter reaction, the Beckmann rearrangement and peptide formation based on easily accessible pentaco-ordinate spirophosphoranes of the type (3) (6 - ). 

Hydroxy-compound Predicted structures of products Products actually obtained by condensation with ... 

Synthesis The synthesis uses rather more vigorous conditions than those which gave the (3-hydroxy carbonyl compounds. In fact (Bull. Chem. Soc. Japan, 1 952, 25, 5k, Chem. Abs., 195 ) A 5143) you can either treat the [3-hydroxy compound with HCl in acetic acid or do the condensation in base ... 

Condensations are some of the most important enolate reactions of carbonyl compounds. Condensations combine two or more molecules, often with the loss of a small molecule such as water or an alcohol. Under basic conditions, the aldol condensation involves the nucleophilic addition of an enolate ion to another carbonyl group. The product, a /3-hydroxy ketone or aldehyde, is called an aldol because it contains both an aldehyde group and the hydroxy group of an alcoho/. The aldol product may dehydrate to an a,/3-unsaturated carbonyl compound. 

The condensation of aldehydes and ketones with halo esters may lead directly to olefinic acids and esters by dehydration of the intermediate /S-hydroxy compounds (Reformatsky). ° More often, the hydroxy esters are isolated and purified prior to dehydration (method 103). 

Olefinic aldehydes and ketones result from the dehydration of the corresponding /5-hydroxy compounds. The availability of olefinic compounds by this method is subject to the limitations of the aldol condensation (method 102) and the mode of dehydration. The tendency for dehydration to a conjugated system (a,/S-olefinic compounds) is not as pronounced as is generally believed. 

Pentafluorophenyl 61 and 4-oxo-3,4-dihydrobenzotriazin-3-yl 65 esters (see Table 16) can be obtained from acid 59 and hydroxy compounds using thionyl chloride the intermediate is the Fmoc amino acid chloride 64 (Scheme 17). In the case of the pentafluorophenyl esters 61, the acid chloride 64 is generated in the absence of the nucleophile and acylation is promoted in the presence of pyridine. While in the case of the 4-oxo-3,4-dihydrobenzotriazin-3-yl esters 65, condensation is achieved by heating the reactants in refluxing dichloromethane. The method is not applicable to derivatives with acid-sensitive side-chain protectors. 

The most common method for the preparation of pyrazoles from other heterocycles is from pyranone-type compounds. Condensation of 2,3-dihydro /7-pyran -ones 787 with various aryl hydrazines in the presence of montmorillonite KSF clay under mild conditions proceeded rapidly to afford enantiomerically pure 5-substituted pyrazoles 788 (Equation 172) <2004TL6033>. Comparable results were obtained when arylhydrazines were reacted with 2-formyl glycals under microwave irradiation <2004TL8587>. Phenylhydrazine and hydrazine were reacted with 3-acetyl-4-hydroxy-6-methyl-2/7-pyran-2-one to afford 4-acetoacetyl-3-methylpyrazolin-5-ones, which were employed in the synthesis of bipyrazoles and pyrazoloisoxazoles <1999JHC1291>. Reaction of 3,3-dialkyl-6-(trifluoromethyl)-2,3-dihy-dro -pyrones with hydrazine hydrate afforded 3-(trifluoromethyl)-5-substituted-pyrazoles <1998RCB1365>. 

DinitrobenzoyI chloride. Place in an eight-inch tube 2 g of 3,5-dinitrobenzoic acid and 4 g of phosphorus pentachloride. Heat in the hood with a small smoky flame for five minutes. In the beginning the tube is heated to start the reaction and thereupon the flame is removed until the reaction has subsided. Then the flame is adjusted so that the vapors condense at about the middle of the tube. Allow to cool for one minute and pour carefully into a small evaporating dish. Cool and transfer the sohd to a paper drying disc or to several filter-paper circles. Press with the spatula so as to force the phosphorus oxychloride into the absorbent medium. After ten minutes transfer the crude 3,5-dinitrobenzoyl chloride into a small bottle or tube. The crude material is satisfactory for the preparation of derivatives of the lower hydroxy compounds. 

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