Carbonyl compounds enolizable

In mordant dyes, phenols, naphthols, and enolizable carbonyl compounds, such as pyrazolones, are generally the couplers. As a rule, 2 1 metal complexes are formed ia the afterchroming process. A typical example of a mordant dye is Eriochrome Black T (18b) which is made from the important dyestuff iatermediate nitro-l,2,4-acid, 4-amiQO-3-hydroxy-7-nitro-l-naphthalenesulfonic acid [6259-63-8]. Eriochrome Red B [3618-63-1] (49) (Cl Mordant Red 7 Cl 18760) (1, 2,4-acid — l-phenyl-3-methyl-5-pyrazolone) is another example. The equiUbrium of the two tautomeric forms depends on the nature of the solvent. 

The reaction can be performed with base catalysis as well as acid catalysis. The former is more common here the enolizable carbonyl compound 1 is depro-tonated at the a-carbon by base (e.g. alkali hydroxide) to give the enolate anion 5, which is stabilized by resonance ... 

The enolate anion 1 may in principle be generated from any enolizable carbonyl compound 4 by treatment with base the reaction works especially well with /3-dicarbonyl compounds. The enolate 1 adds to the a ,/3-unsaturated compound 2 to give an intermediate new enolate 5, which yields the 1,5-dicarbonyl compound 3 upon hydrolytic workup ... 

Corey and Chaykovsky were the first to investigate the reaction of dimethyl sulphoxide anion (dimsyl anion) with aldehydes and ketones400,401. They found that the reaction with non-enolizable carbonyl compounds results in the formation of /1-hydroxyalkyl sulphoxides in good yields (e.g. Ph2CO—86%, PhCHO—50%). However, with enolizable carbonyl compounds, particularly with cycloalkanones, poor yields of hydroxyalkyl products are observed (e.g. camphor—28%, cyclohexanone—17%, but... 

In the presence of a catalytic amount of triethylamine, a readily enolizable carbonyl compound like acetylacetone (25) can undergo a Michael-type addition onto the triple bond of 23 with C-C bond formation, and subsequent 1,2-addition of the hydroxy group with elimination of an alcohol (MeOH or EtOH) to eventually yield a pyranylidene complex 28 (mode E) [29]. The most versatile access to / -donor-substituted ethenylcarbene complexes 27 is by Michael-type additions of nucleophiles, including alcohols [30-32], primary... 

Allyl vinyl ethers have been prepared using the ylide (101) but only from non-enolizable carbonyl compounds. The ethers rearrange on heating to give a-allyl aldehydes, e.g. (102). 

The Mannich reaction is the condensation of an enolizable carbonyl compound with an iminium ion.180 It is usually done using formaldehyde and introduces an a-dialkylaminomethyl substituent. 

Trimethylsilylation of enolizable carbonyl compounds and alcohols has also been accomplished by the fluoride ion promoted reaction with hexamethyldisilane and ethyl trimethylsilylacetate [48, 49], with high stereospecificity giving Z-enol ethers from ketones [50]. l-Trimethylsilyl-(l-trimethylsilyloxy)alkanes, produced from the reaction of aldehydes with hexamethyldisilane, undergo acid-catalysed hydrolysis during work up to yield the trimethylsilylcarbinols [51]. In the case of aryl aldehydes, the initially formed trimethylsiloxy carbanion produces the pinacol (Scheme 3.1). 

The synthetically most valuable intermediate in heterofullerene chemistry so far has been the aza[60]fulleronium ion C59N (28). It can be generated in situ by the thermally induced homolytic cleavage of 2 and subsequent oxidation, for example, with O2 or chloranil [20-24]. The reaction intermediate 28 can subsequently be trapped with various nucleophiles such as electron-rich aromatics, enolizable carbonyl compounds, alkenes and alcohols to form functionalized heterofullerenes 29 (Scheme 12.8). Treatment of 2 with electron-rich aromatics as nucleophilic reagent NuH in the presence of air and excess of p-TsOH leads to arylated aza[60]fullerene derivatives 30 in yields up to 90% (Scheme 12.9). A large variety of arylated derivatives 30 have been synthesized, including those containing cor-annulene, coronene and pyrene addends [20, 22-25]. 

Grignard reagents add with difficulty to imines derived from enolizable carbonyl compounds. The activation of the C=N bond can be achieved either by attachment of an electron-with drawing group or A-coordination with a Lewis acid . The use of a catalytic amount of the soluble rare-earth metal complex LnCl3 2LiCl allows the addition of... 

This reagent is useful due to its low acidity and basicity, allowing it to be used in the presence of easily enolizable carbonyl compounds. The reagent will selectively react with a simple carbonyl in the presence of a carboxyl-type carbonyl group. 

Among the oxidants that have been used to generate radicals, manganese (HI) acetate has emerged as a powerful reagent to mediate radical cyclizations.147 The manganese(III) acetate-mediated oxidation of enolizable carbonyl compounds is one of the best methods available for the cyclization of electrophilic radicals. The substrates are vety easily prepared by standard alkylation and acylation reactions. Radicals are formed with high selectivity by oxidation of acidic C—H bonds, and, because the reaction is an oxi-... 

One-electron oxidation systems can also generate radical species in non-chain processes. The manganese(III)-induced oxidation of C-H bonds of enolizable carbonyl compounds [74], which leads to the generation of electrophilic radicals, has found some applications in multicomponent reactions involving carbon monoxide. In the first transformation given in Scheme 6.49, a one-electron oxidation of ethyl acetoacetate by manganese triacetate, yields a radical, which then consecutively adds to 1-decene and CO to form an acyl radical [75]. The subsequent one-electron oxidation of an acyl radical to an acyl cation leads to a carboxylic acid. The formation of a y-lactone is due to the further oxidation of a carboxylic acid having an active C-H bond. As shown in the second equation, alkynes can also be used as substrates for similar three-component reactions, in which further oxidation is not observed [76]. 

The intermolecular Mannich reaction combines an aldehyde, an amine and an enolizable carbonyl compound for the one-pot synthesis of yfi-amino ketones or... 

The asymmetric alkylation of cyclic ketones, imines of glycine esters, and achiral, enolizable carbonyl compounds in the presence of chiral phase-transfer organoca-talysts is an efficient method for the preparation of a broad variety of interesting compounds in the optically active form. The reactions are not only highly efficient, as has been shown impressively by, e.g., the synthesis of enantiomerically pure a-amino acids, but also employ readily available and inexpensive catalysts. This makes enantioselective alkylation via chiral phase-transfer catalysts attractive for large-scale applications also. A broad range of highly efficient chiral phase-transfer catalysts is also available. 

This multi-component condensation of a nonenolizable aldehyde, a primary or secondary amine and an enolizable carbonyl compound affords aminomethylated products. The iminium derivative of the aldehyde is the acceptor in the reaction. 

Pyranylidene Complexes by C-Addition of Enolizable Carbonyl Compounds... 

Addition of carbon nucleophiles to the C=C bond of a compound la,b includes reactions of enolizable carbonyl compounds, enol ethers, and ena-mines, as well as lithium alkyls and zinc alkyls. Condensation of the enolizable ketone 68 with la,b (M = Cr, W)26 is induced, for example, by catalytic amounts of triethylamine in pentane and under these conditions affords a 90% yield of crystalline pyranylidene complex 57 directly from the reaction mixture.102 This reaction proceeds via the 2-ethoxy-l-metallatriene L, which, because of the presence of triethylamine, rapidly undergoes ring closure to the pyranylidene (pyrylium ylide) complex 69 by 1,6-elimination of ethanol (Scheme 22). Chromanylidene complexes 71 are obtained from condensation of a /3-tetraIone 70 (R = H, OMe) with compound 1a,b. 

Addition of enolizable carbonyl compounds to the C=C bond of (1-alkynyl)carbene complexes can proceed by C- or O-addition of the enol unit. The C/O ratio depends very much on the substrate as well as on the reaction conditions. Reaction of cyclic 1,3-diketones 72 in diethyl ether in the presence of catalytic amounts of Et3N results in the formation predominantly of (red) divinyl ethers 73 (by O-alkylation) together with smaller amounts of (blue) pyranylidene complexes 74 by (C-alkylation) (Scheme 23).26103 For related reactions, see Scheme 67. 

The Fischer indole synthesis is commonly recognized as one of the most powerful and versatile tools for construction of indoles, as reflected by the amount of recent publications in which it has been used successfully. The usual approach involves initial preparation of a phenylhydrazone 323 from a suitable phenylhydrazine and an enolizable carbonyl compound, followed by an acid-induced cyclization to the target indole 324, featuring a [3,3]-sigmatropic rearrangement as the key step (Scheme 38). Some selected new examples of indoles prepared using standard Fischer conditions are collected in Table 2. 

Thioacetalizfltion.23 Aldehydes and ketones react with alkylthiols and alkanedithiols in the presence of catalytic amounts of TiCl4 in CHC13 at 28° to form thioacetals and -ketals in >90% yield. The reaction is satisfactory even with readily enolizable carbonyl compounds. 

Lithiation of vinylic sulfones. Phenyl vinyl sulfones (1), prepared as indicated, react with methyllithium regiospecifically at — 95° at the a-vinyl position to give the lithium derivatives 2. As expected, 2 can be alkylated to give 3. The reaction of 2 with enolizable carbonyl compounds proceeds more satisfactorily by prior conversion to the vinylic Grignard reagent a. This sequence constitutes a route to disubstituted alkenes, since a sulfone group is reductively cleaved by sodium amalgam (7, 326). ... 

Aliphatic amines are mainly converted to a-substituted products [99,100], whereby especially the a-methoxylation leads to valuable reagents for synthesis. The intermediate iminium salts can be directly trapped by silyl enol ethers to form Mannich bases [108]. If the a-position is blocked or steric conditions favor it, N,N coupling to hydrazo or azo compounds occurs (Table 5, numbers 17-19). 1,1-Disubstituted hydrazines are dimerized to tetrazenes in fair to excellent yields (Table 5, numbers 20-24). The intermediate diaze-nium ions can attack enolizable carbonyl compounds to form aza-Mannich bases [109]. Arylazonaphthols undergo anodic oxidation, producing radical cations. These couple to biphenylbisazo compounds (up to 34%) or can be trapped by anisidine to form azodiphe-nylamines (up to 74%) [110a]. 

In the proline-catalyzed aldol reactions, enolizable achiral aldehydes and ketones are transformed into the corresponding enamines, which can then react with less enolizable carbonyl compounds, even in one-pot protocols. These reactions, unlike most catalytic aldol reactions, do not require preformed enolates, and constitute direct aldol reactions. 

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