Active methylene compounds coupling with

With certain active methylene compounds, particularly with active methinyl compounds, diazonium salts may couple to form azo compounds. Several intramolecular couplings of diazonium salts with ortho substituents bearing an active methylene group give rise to cinnolines, a class of cyclic azo compounds (the Borsche, von Richter, and Widman-Stoermer syntheses.)... 

Alkylidene-2,3-dihydropyridazines (124) are synthesized by coupling of 3-thiomethyl-pyridazinium salts with active methylene compounds in the presence of potassium carbonate in DMF (Scheme 39) (79TL4837). 

C-coupling is of outstanding importance in the azo coupling reaction for the synthesis of azo dyes and pigments. An aromatic or heteroaromatic diazonium ion reacts with the so-called coupling component, which can be an aromatic primary, secondary, or tertiary amine, a phenol, an enol of an open-chain, aromatic, or heteroaromatic carbonyl compound, or an activated methylene compound. These reactions at an sp2-hybridized carbon atom will be discussed in Chapter 12. In the... 

A further example of an azo coupling reaction with an activated methylene compound (12.91), followed by ring closure to give a pyridazine derivative (12.92) in good yield (66%) was decribed by Gewald and Hain (1984). The reductive treatments of 12.92 give the pyrrole compounds 12.93 and 12.94 in 70% yield (Scheme 12-45). 

The thiazine dyes used in the preparation of this type of leuco are obtained through oxidative coupling of phenothiazine with an active methylene compound or an aniline. The reduction of the dye 23 with zinc powder in acetic acid is straightforward.9 Treatment of the leuco 24 with acetic anhydride at 40°C yields a more air stable leuco 25.9 Addition of arylsulfinic acid to thiazine dyes such as 26 produces directly leuco dyes such as 27.Sb... 

The consecutive reaction of vinyl halides and alkenes with activated methylene systems [42] in the presence of a palladium catalyst and phase-transfer catalyst results from the addition of the methylene carbanion with the initially formed Heck product (Scheme 6.31) an intramolecular version of the reaction leads to the formation of bicycloalk-l-enes (Scheme 6.31) [42], The analogous combined coupling reaction of iodoarenes and activated methylene compounds with non-conjugated dienes under similar conditions forms the monoalkene (Scheme 6.31) [43]. 

The electrogenerated Mn(lll)-assisted coupling of various olefins with active methylene compounds proceeds by indirect electrooxidation with a small amount of Mn(OAc)2 in the presence or absence of Cu(OAc)2 [196]. The Mn(Ill)-assisted carboxymethylation of styrenes (142) affords y-aryl-y-lactones (143) in good current yields (Scheme 57) [194, 195, 206, 207], (Table 9). 

The linear telomerization reaction of dienes was one of the very first processes catalyzed by water soluble phosphine complexes in aqueous media [7,8]. The reaction itself is the dimerization of a diene coupled with a simultaneous nucleophilic addition of HX (water, alcohols, amines, carboxylic acids, active methylene compounds, etc.) (Scheme 7.3). It is catalyzed by nickel- and palladium complexes of which palladium catalysts are substantially more active. In organic solutions [Pd(OAc)2] + PPhs gives the simplest catalyst combination and Ni/IPPTS and Pd/TPPTS were suggested for mnning the telomerizations in aqueous/organic biphasic systems [7]. An aqueous solvent would seem a straightforward choice for telomerization of dienes with water (the so-called hydrodimerization). In fact, the possibility of separation of the products and the catalyst without a need for distillation is a more important reason in this case, too. 

B. Coupling of Diazonium Salts with Active Methylene Compounds... 

Coupling of amidrazones with phenols, active methylene compounds, or aromatic amines [116] (Eq. 57). 

The Rh/tppts catalysed C-C coupling reaction (Figure 17) has a broad scope and numerous conjugated dienes e.g. isoprene and P-famesene can be used as starting materials with other active methylene compounds e.g. acetylacetone and barbituric acid.506 Figure 18 depicts the Rh/tppts/Na2C03-catalysed isopreny-lation of barbituric acid which proceeds at room temperature in an H20/MeOH (75/25) solvent mixture.506... 

Coupling of aryl bromides with diethyl sodiomalonate. CuBr is the most effective Cu(I) catalyst for effecting coupling of aryl iodides or bromides with the sodium salts of active methylene compounds such as diethyl sodiomalonate. Coupling is facilitated by ori/io-substituents in the halide, particularly nitro, carbomethoxy, and methoxy groups.1 This reaction has been adapted to synthesis of benzofurane-2-ones.2... 

Although arylation or alkenylation of active methylene compounds can be carried out using a Cu catalyst, the reaction is sluggish. However, the arylation of malononitrile (390) or cyanoacetate proceeds smoothly in the presence of a base and Pd catalysts [189], Tetracyanoquinodimethane (392) is prepared by the coupling of / -diiodoben-zene with malononitrile (390) to give 391, followed by oxidation [190], Presence of the cyano group seems to be essential for intermolecular reactions. However, the intramolecular arylation of malonates, / -keto esters and /i-diketones proceeds smoothly [191]. The bromoxazole 393 reacts with phenylsulphonylacetonitrile (394)... 

Anodic oxidation of Mn(OAc)2 (catalytic amounts) in the presence of nonacti-vated alkenes and ethyl acetoacetate provides a route to dihydrofurans (cf, 6, 356). This electrooxidation of Mn(OAc)2 has been extended to coupling of activated methylene compounds with alkenes and dienes. 

The behavior of bis(heteroaryl)methanes in which the heterocycle was an electron-withdrawing group was similar to that typically exhibited by active methylene compounds. Bis(2-benzothiazolyl)methane and bis(2-(5-ethoxycarbonyl-4-methyl)thiazolyl)methane readily underwent azo-coupling with benzenediazonium chloride, nitrosation with nitrous acid and condensation with aromatic aldehydes under mildly basis conditions, such as in the Knoevenagel procedure. [94G301]... 

The coupling of aryl halides with active methylene compounds, such as mal-onitriles and cyanoacetates, is of increasing interest due to its inherent difficulty and the interest of the resulting products as synthetic intermediates in the preparation of bio active [36,37], heterocyclic [38,39] or conducting compounds [40]. Bulky NHCs have been found to be excellent ligands in the coupling of aryl halides with malonitrile [41] in hot pyridine using NaH as base (Scheme 7). 

Hashida et al. also found a good linear relationship for the azo coupling rates of 11 P-dicarbonyl compounds and the pK values of these C-acids. However, two dicarbonyl compounds with a trifluoromethyl group attached to one of the carbonyl functions were exceptions. Furthermore, no relationship between log k and pK could be observed for azo coupling reactions of active methylene compounds other than p-dicarbonyls. 

Amino-3,5-dinitropyrazole underwent diazotization to afford 4-diazo-3,5-dinitropyrazole, which reacted with active methylene compounds to give azo coupling products <1997MC58>. 

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