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Carbonyl compounds homologation

The reactivity of 2-methylselenazole toward carbonyl compounds is the same as its thiazoie homolog. Reaction of 2,4-dimethylselenazole with benzaldehyde in the presence of anhydrous zinc chloride as catalyst gives 4-methyl-2-styrylselenazoie [m.p. 74-75 C (19)] (Scheme 43). [Pg.249]

Air-stable palladium(O) catalyst, [(Cy3P)2Pd(H)(H20)]BF4, catalyses carbonylation of propargylic alcohols to generate dienoic acids and esters (equation 167)286. Since propar-gyl alcohols are obtained from carbonyl compounds by acetyhde addition reactions, this sequence constitutes a three-carbon homologation. a-Allenic alcohols are converted to tt-vinylacrylic acids under similar conditions (equation 168)287. [Pg.456]

If, however, PEG-400 is employed as the solvent and phase transfer catalyst, under a nitrogen atmosphere, then the monoacid is obtained in good yield. Since vinylic dibromides are easily synthesized from carbonyl compounds, this constitutes a valuable method for oxidative homologation(19). [Pg.12]

Reaction of carbonyl compounds with aliphatic diazo compounds to deliver homologated ketones. [Pg.94]

MetaUation of 4-hetero-substituted dibenzothiins (427) with lithium, catalyzed by 4,4 -di-f-butylbiphenyl (equation 122), breaks one of the C—S bonds. Quenching with carbonyl compounds leads to the corresponding thiophenols (428) that may be cyclized to the homologous seven-membered heterocycles (429). The products can be characterized by IR, H and NMR spectroscopies and MS . ... [Pg.416]

Finally, the addition of the carbanion of 1-chloroalkyl p-tolyl sulfoxides 154 to carbonyl compounds gave the adducts 155, which were treated with alkyllithium such as f-C4H9Li to afford the one-carbon homologated carbonyls compounds 158, from their lithium enolate forms 157, having an alkyl group at the a-position, via the carbenoid /S-alkoxides 156 (equation 53) °. [Pg.484]

A Wittig reaction of the 17-oxo-7(8-lla)-aheo-compound (106) led to the Ai7 20) compound (107). Homologation of carbonyl compounds to carboxylic... [Pg.241]

A one-carbon homologation of carbonyl compounds is an important and extensively used method for the preparation of desired carbonyl compounds . One-carbon ring-expansion or one-carbon homologation of ketones or aldehydes via a S-oxido car-benoid is a representative example of the homologation, but few methods have been reported . [Pg.760]

Diethyl [(2-tetrahydropyranyloxy)methyl]phosphonate is useful in the Wlttig-Horner synthesis of enol ethers, which are intermediates in one-carbon homologations of carbonyl compounds. This procedure is an adaptation of a general method for making dialkyl hydroxymethylphosphonates. An 0-tetra-hydropyranyl derivative also has been made from dibutyl hydroxymethyl -phosphonate, and diethyl hydroxymethylphosphonate has been O-silylated with tert-butylchiorodimethylsilane and imidazole. Another useful congener in this series has been prepared by an Arbuzov reaction of methoxyethoxymethyl (HEM) chloride and triethyl phosphite. [Pg.83]

See also page 403, Section 6, for the synthesis of a,/3-unsaturated nitriles, carboxylic acids and derivatives, and page 1711, Section 4, for the homologation of carbonyl compounds. [Pg.1681]

All the enthalpies of formation for acyclic aliphatic aldehydes and ketones which are discussed in this section are tabulated by Pedley and coworkers16. The number of these carbonyl compounds whose enthalpies of formation have been measured are few compared to the abundant data available for alkenes and so there are fewer decisions to make on which data to include. However, we then lack the means to make the comprehensive analyses we would prefer. The demonstrated linearity34 of the enthalpies of formation of the members of a homologous series vs the number of carbon atoms, nc, in the molecules provides an excellent visual method for determining the quality of the data any enthalpy of formation which deviates significantly from linearity is of questionable reliability. The linear relationship can be expressed as in equation 4 and the results of the regression analyses of this equation for aldehydes and ketones appear in Table 4. [Pg.575]

This monograph covers the period 1989-1995 and is partially an update of the work by Schaumann1. The scope is essentially the same, attention being focused primarily on thioaldehydes (thials) and thioketones (thiones). In keeping with the spirit of Reference 1, only some new developments in the field of thioketene, hetero cumulene and thioquinone chemistry are considered. Because of the fast evolution in the field, the spirit is somewhat different and physicochemical and theoretical topics are emphasized. Whenever possible, systematic comparisons with homologous carbonyl compounds, a natural yardstick, are carried out. [Pg.1357]

Table 16 summarizes these results together with data from other sources for the homologous carbonyl compounds. Other values are given elsewhere39. Figure 2 is a plot of GB (XCSY) vs GB (XCOY) obtained from the data given in Table 16. [Pg.1459]

Other major homologation processes are the nitroaldol reaction, arising from the reaction between a nitronate anion and a carbonyl compound, and a Michael addition reaction. [Pg.768]

Homologated aldehydes.1 The anion of the reagent converts carbonyl compounds into the I I IP cnol other of onc-carbon homologated aldehydes (equation I). [Pg.433]

Enamidines (2). Lithiation of 1 followed by treatment with aldehydes or ketones results in Peterson olefination to give a mixture of isomeric enamidines (2) in good yield. These enamidines can be used to convert the carbonyl compounds used in (heir preparation to homologated amines, aldehydes, and ketones. Conversion to a mclhylaminc involves reduction with sodium borohydride (pH 6) to an aminal, which is then hydrolyzed by dilute acid. The sequence can be carried out from 1 without isolation of any intermediates (equation I). [Pg.516]

In the past, Darzens methodology was primarily used for the synthesis of aldehydes and ketones, as a homologation reaction without any consideration of stereocontrol in the epoxide formation. For this sequence, saponification of the a,P-epoxy ester followed by decarboxylation gives the substituted carbonyl compound ... [Pg.92]

Enamines are highly valued intermediates in organic synthesis. Almost invariably they are prepared by reaction of a carbonyl compound with a secondary amine. In principle, another attractive route to enamines could be based on construction of the double bond by a Wittig- or Horner-Wittig reaction. The enamines J thus obtained could be easily converted into the corresponding homologous aldehydes, if desired fitted with an extra electrophilic substituent at the original carbonyl carbon atom. [Pg.47]

There has been one report of an rj1 -pentadienyl complex of a transition element, Cp2Zr(2-MeC5H6)2, prepared from Cp2ZrCl2 and 2-methyl-pentadienylpotassium (155). Cp2ZrHCl, however, give -complexes of 1,3-pentadiene and its higher homologs, when treated with pentadienyl-potassiums. The reactions of these products with alkenes, alkynes, dienes, and carbonyl compounds are synthetically important (156). [Pg.143]

Fig. 17.69. Two-step sequence for the conversion of a ketone into the homologous nitrile ("reductive cyanation of a carbonyl compound"). In the second step of the reaction the diazene anion G is generated and decomposes in a similar way as the diazene anion D in the Wolff-Kishner reduction of Figure 17.67 and the diazene anion G of the semicarbazone reduction in Figure 17.68. Fig. 17.69. Two-step sequence for the conversion of a ketone into the homologous nitrile ("reductive cyanation of a carbonyl compound"). In the second step of the reaction the diazene anion G is generated and decomposes in a similar way as the diazene anion D in the Wolff-Kishner reduction of Figure 17.67 and the diazene anion G of the semicarbazone reduction in Figure 17.68.

See other pages where Carbonyl compounds homologation is mentioned: [Pg.105]    [Pg.877]    [Pg.165]    [Pg.323]    [Pg.877]    [Pg.138]    [Pg.382]    [Pg.382]    [Pg.423]    [Pg.131]    [Pg.117]    [Pg.99]    [Pg.439]    [Pg.175]    [Pg.123]    [Pg.357]    [Pg.1459]    [Pg.598]    [Pg.47]    [Pg.201]    [Pg.64]    [Pg.64]    [Pg.414]    [Pg.320]   


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