Hydrogen condensation with elimination

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). 

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

Preceding condensation with elimination of hydrogen bromide... 

Benzoin -As a small cjnantity of potassium cyanide is (apable of converting a large quantity of benzaldehyde into bciv/oin, the action of the cyanide has been explained as follows. The potassium cyanide first reacts with the aldehyde and forms a cyanhydnn, which then condenses with another molecule of aldehyde, hydrogen cyanide being finally eliminated (Lapwortbj,... 

Whereas most of the known silylamines containing both a silicon halogen and nitrogen hydrogen unit undergo rapid condensation with HC1 elimination [11], transition metal substitution of the silicon provides unexpected high thermal stability. Compounds of this type are available via reaction of the dichlorosilyl complexes 18a-c with bulky primary amines to generate 19a-c (Eq. (4)). 

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... 

It will be seen that only an aldehyde with at least one a-hydrogen can condense with itself or with another aldehyde. This latter, however, need have no particular structure. Condensing agents stronger than those mentioned above eliminate water if possible, after condensation. Two a-hydrogen atoms in an aldehyde are necessary for this change (see Reaction XXIV.). 

Schmidt and Wernicke74 have described a synthesis of digitalose starting with D-fucose dibenzyl mercaptal, which on condensation with acetone yielded the 4,5-isopropylidene derivative (LXXIV). Elimination of the dibenzyl mercaptal residues with mercuric chloride and cadmium carbonate in methanol gave 4,5-isopropylidene-D-fucose dimethylacetal (LXXV), from which the 2-benzyl ether was obtained on treatment with sodium and benzyl chloride. Methylation produced 2-benzyl-3-methyl-4,5-iso-propylidene-D-fucose dimethyl acetal (LXXVI), from which the iso-propylidene group was eliminated on treatment with methanolic hydrogen chloride, which also effected glycopyranoside formation (LXXVII). The... 

In the presence of acids, continued Griess and Harrow,8 at least two other compounds were formed and could be isolated when a reaction mixture similar to that described in their first paper was allowed to stand for a month in a warm place. The less soluble compound mentioned earlier was named anhydrogluco-o-diaminobenzene. It was formed by the condensation of one molecule of glucose with one molecule of o-phenylenediamine two molecules of water and two hydrogen atoms were eliminated during the reaction. They formulated the product N=CH... 

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. 

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... 

Furfural (18) was oxidized to give the butenolide 19, which on Michael condensation with diethyl ethylmalonate afforded lactone 20. Hydrolysis of 20 yielded the dilactone 21. This was treated with ethanol in the presence of sulfuric acid. The isomer mixture obtained was separated by preparative thin-layer chromatography, yielding 4-ethoxy-3-ethoxycarbonylmethyl-2-ethyl-4-butanolide (22). Elimination of ethanol, with the aid of p-amino-benzenesulfonic acid, gave 2-(3//)-furanone 23 the 2-(5//)-furanone isomer 24 was obtained with the aid of orthophosphoric acid. Both isomeric esters gave the acid 25 after hydrolysis, which on catalytic hydrogenation afforded m-3-carboxymethyl-2-ethyl-4-butanolide 26, identical to homopilopic acid. This synthesis of homopilopic acid differs from earlier syntheses because the less stable cw-2,3-disubstituted butanolide (26) is formed in the last step. 

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