Condensation with elimination of hydrogen

Without additional reagents Condensation with elimination of hydrogen chloride... 

Preceding condensation with elimination of hydrogen bromide... 

In acidic medium, the reaction intermediate is probably the enethiol (17). An example of such a reaction is the condensation of the thio-DMF, in the presence of phosphorus oxychloride, with a methyl group at the 2-position. An enamine is obtained, in poor yields, with elimination of hydrogen sulfide (7lJCS(Q2829). 

When 2-acetylphenyl tellurium bromide and aromatic aldehydes were refluxed in acetic acid in the presence of piperidine, 2-benzylidene-3-oxo-benzotellurophenes were formed in 80% yields4. These reactions were proposed to proceed via 2-(3-aryl-l-oxoprop-2-en-l-yl)-phenyl tellurium bromides that cyclize with elimination of hydrogen bromide. However, 3-oxo-2,3-dihydrobenzotellurophene cannot be ruled out as the intermediate which then condenses with the aromatic aldehydes2, because 2-acetylphenyl tellurium bromide is known to cyclize to form 3-oxo-2,3-dihydrobenzoteIIurophene2,3. 

It was soon discovered that ferrocene condenses with aldehydes under suitable conditions either condensation with elimination of water or carbinol formation may occur 136,166, 202). Further, base-catalyzed aldol and Claisen condensations involving the -hydrogen atom of acetyl-ferrocene can be carried out 100). 

Borazines are generally prepared by condensations between amines and boron hydrides or halides at up to 200 , with elimination of hydrogen or hydrogen halide ... 

The most widely applied precursors for the synthesis of monocyclic NHPs are a-diimines which can be converted to the target heterocycles either in a two-step reaction sequence involving two-electron reduction of the diimine to an enediamide, enediamine, or a-aminoamine and subsequent condensation with PC13 [18-20] or a dichlorophosphine RPC12 [21], or via direct base-promoted reaction with PC13 [20, 22], The latter reaction involves addition of a P-Cl bond to each imine moiety followed by base-promoted elimination of hydrogen chloride leading to 2,4-dichloro-... 

Chain growth is then thought to occur via condensation of these groups with elimination of water and addition of hydrogen ... 

Condensation polymerizations (polycondensations) are stepwise reactions between bifunctional or polyfunctional components, with elimination of small molecules such as water, alcohol, or hydrogen and the formation of macromo-lecular substances. For the preparation of linear condensation polymers from bifunctional compounds (the same considerations apply to polyfunctional compounds which then lead to branched, hyperbranched, or crosslinked condensation polymers) there are basically two possibilities. One either starts from a monomer which has two unlike groups suitable for polycondensation (AB type), or one starts from two different monomers, each possessing a pair of identical reactive groups that can react with each other (AABB type). An example of the AB type is the polycondensation of hydroxycarboxylic acids ... 

The general principle usually involves contact of an aldehyde or mixtures of aldehydes with ammonia at high temperature in the presence of an acidic catalyst. Aluminosilicate catalysts have been used (80USP4220783). A series of condensation reactions occurs with elimination of water and hydrogen and mixed products usually result. Acetaldehyde gives... 

The use of aluminium chloride for bringing about condensation by the elimination of hydrogen chloride was first made known by Friedel and Crafts in 1877, T/ho applied it to the preparation of benzene hydrocarbons by the treatment of benzene with alkyl chlorides, in the presence of anhydrous aluminium chloride ... 

However, over Ni-kieselguhr in the absence of solvent or in ether and methylcyclo-hexane 32-33% of a diester, ethyl 3-(3 -hydroxybutyryloxy)butyrate (8), was produced along with 68-67% of ethyl 3-hydroxybutyrate and small quantities of dehydroacetic acid, and over copper-chromium oxide 16% of the diester and 7% of dehydroacetic acid were formed in the absence of solvent. It was suggested that the diester is formed through the hydrogenation of the intermediate 9, which results from 2 mol of acetoacetic ester with elimination of 1 mol of ethanol and that the condensation reaction is reversible (Scheme 5.6). Hence, the formation of the diester is depressed in the hydrogenation in ethanol.121 The reaction pathway in Scheme 5.6 has... 

An efficient and practical two-step [4-1-1] oxazole synthesis utilizes the condensation of serine methyl ester with ethyl imidate 193 to give an intermediate oxazoline 194. Treatment of 194 under basic conditions brings about elimination of hydrogen chloride to give oxazole 195 in high yield (Scheme 54) <20010PD37>. 

In Stork s synthesis (148), 5 - methyl - 6 - methoxy - 1 - tetralone (CLXXXIV) was converted into the tricyclic intermediate CLXX XVII in several steps involving condensation with dimethyl carbonate, addition of methyl isopropenylketone, and cyclization to the a, -unsaturated ketone CLXXXVI, followed by catalytic hydrogenation, replacement of the hydroxyl group in the resulting dihydro alcohol by a chlorine atom on treatment with phosphorus oxychloride in pyridine solution, and elimination of hydrogen chloride by methanolic sodium methoxide. 

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