Pyridine as base

The Glaser coupling reaction is carried out in aqueous ammonia or an alcohol/ammonia solution in the presence of catalytic amounts of a copper-I salt. The required copper-II species for reaction with the acetylide anion R-C=C are generated by reaction with an oxidant—usually molecular oxygen. For the Eglinton procedure, equimolar amounts of a copper-II salt are used in the presence of pyridine as base. 

The term Knoevenagel reaction however is used also for analogous reactions of aldehydes and ketones with various types of CH-acidic methylene compounds. The reaction belongs to a class of carbonyl reactions, that are related to the aldol reaction. The mechanism is formulated by analogy to the latter. The initial step is the deprotonation of the CH-acidic methylene compound 2. Organic bases like amines can be used for this purpose a catalytic amount of amine usually suffices. A common procedure, that uses pyridine as base as well as solvent, together with a catalytic amount of piperidine, is called the Doebner modification of the Knoevenagel reaction. 

Another tetrahydroporphyrin derivative, porphodimethene (7), which consists of two dipyr-rylmethene halves is obtained in the photoreduction of magnesium-containing chlorophyll a (6) with hydrogen sulfide3211 42 as reductant and pyridine as base. 

FIGURE 8.5 Synthesis of p-nitroanilides by aminolysis (A) of the mixed anhydride obtained with M = A-methylmorpholine as base,14 (B) of the dichlorophosphoric anhydride obtained with P = pyridine as base and solvent, [Rijkers et al., 1991] and (C) by reaction with p-nitrophenylisocyanate. (Nishi Noguchi, 1973). 

In the approach of Puddephatt et al., the P-phenyl-phosphonitocavitand 2 was obtained by the reaction of phenylphosphonous chloride on re-sorc[4]arene lb (1, R=CH2CH2C6H5) in presence of pyridine as base. The reaction is stereoselective and yielded the bowl-shaped molecule 2 with the four P-phenyl groups directed outwards and the four lone pairs directed inwards ini configuration) [45-49] (Scheme 6). Molecular mechanics calculations performed on the six possible isomers of 2, showed that the iiii isomer is preferred and the orientation of one phenyl group toward the macrocyclic cavity is probable iiio isomer), but two or more phenyl groups oriented inwards are highly unlikely [48]. 

Methylenedithiol was used to construct cyclic meat flavor compounds, such as l,3-dithian-5-one 217 <1998FFJ177>. The reaction of the geminal dithiol with a 1,3-dibromide proceeds with pyridine as base in 44% yield (Equation 81). 

Calorimetric studies (86UP1) have shown that the behavior of azoles as acids and bases closely ressembles that of pyridines (as bases). 

Our attempts as well as those of C. C. Price to react 2.4.6-triphenylpyry-lium salts with phosphine, phenylphosphine or tris-hydroxymethyl-phosphine in the hope of isolating phosphorins or their P-substituted derivatives were unsuccessful. In contrast, MarM applying essentially the same principle but using pyridine as base and solvent, succeeded by heating 2.4.6-triphenylpyrylium-tetrafluoro-borate 21 with tris-hydroxymethyl-phosphine 5. He was able to isolate 2.4.6-triphenyl-X -pbosphorin 22, m. p. 171—172 C, as the first X -phosphorin in 20-25% yield. 

Pyridine, as base in dehydration of formamides with phosphorus oxychloride, 41, 13... 

Dihydroxylation of hindered double bonds. The a-pinene derivative 1 (Nopol) is hydroxylated in low yield by osmium tctroxide and f-butyl hydroperoxide. Hydroxylation is effecled in 62% yield by use of 0s04 in combination with trimethylamine N-oxide as oxidant and pyridine as base. This method is generally suitable for hindered alkenes (yields 78-93%). 

The reaction was carried out in CH3CN-Et4NC104 with addition of pyridine as base, using controlled potential electrolysis and a divided cell. The yield of (33) varied greatly, depending on the method of electrolysis. Oxidation of 32 in the presence of pyridine gave 33 in 60-85% yield, whereas the electrolysis without pyridine lowered the yield to 10-20%, and products of hydrolysis, because of accumulation of the acid in the anodic compartment, were identified. The mechanism of the reaction proposed on the basis of electroanalytical results involves the cyclization of the radical-cation or its deprotonation as the rate-determining step.78... 

In contrast to the broad variety of applications of 1 - 4 and 1 3 linked glucans after reaction with (C2 to C4) carboxylic acid anhydrides and chlorides [159], the use of dextran esters of short chain aliphatic acids such as acetates or propionates is rather limited. According to the present knowledge, the commonly applied acetylation of polysaccharides with the acetic acid anhydrides or acetyl chlorides in the presence of triethylamine or pyridine as base does not lead to pure and soluble dextran acetate with significant DS values. In contrast, dextran propionates [160] and butyrates [161] can be... 

Lactonization of e-hydroxy acids. The e-hydroxy acid 1 is converted into the oxazepine 2 in 55% yield by cyanuric chloride and pyridine as base in 55% yield. The combination of cyanuric chloride and triethylamine has been recommended... 

Esterification. The related salt dimethylchloroforminium chloride has been used for esterification (8, 186), but has the disadvantage that alkyl chlorides are also formed as by-products. The salt 1 does not activate an alcohol group and, in the presence of pyridine as base, it effects esterification of acids (even hindered ones) with primary and secondary alcohols in high yield. Esterification with hindered tertiary alcohols is possible, but slow. 

Reaction of the same functionalised imidazolium salt with PdCl produced interesting results [123], In the presence of pyridine as base, the simple palladium(ll) carbene adduct was formed (see Figure 4.42), but when K COj was used as base, activation of the amide functional groups produced the corresponding homoleptic complexes, as a mixture of the cis and trans isomers. 

The synthetic route to acridine-containing polymers is outlined in Scheme I. 9-Methyl acridine (II) was prepared via 9-ethyl-malonate acridine by the method of Campbell et al (14), from 9-chloroacridine (I, Kodak), (mp. 117-8°C from ligroin). 9-(3hydro-xyethyl) acridine (III) was synthesized via the condensation of formaldehyde with II (15) (mp. 154-6°C, from ethanol-water). Metha-cryloylchloride, freshly distilled, was reacted with III in dry THF with pyridine as base to give IV, 2-(9-acridyl) ethylmethacrylate, purified by chromatography with silica gel/toluene to give red gum (IR 5.85 ym ester carbonyl stretch). 

Treatment of the 1,3-diselenonium cations 102a,b-GF3SO3 with malononitrile, using pyridine as base, gave compounds 40a and 40b, which contain the dicyanomethylene acceptor group (Equation 8) <1998T13257>. In the same report, the syntheses of 24, 43, 44, 103, and 104 are described <1998T13257>. 

X = H, Ph, CH3, or COOCH3). Palladium black could also be used as a catalyst, and triethylamine or pyridine as bases. Heck also studied this reaction, and proposed that phenylpalladium was formed by oxidative addition to Pd(0), which was formed by reduction of the Pd(II) (101). 

Oxidation of the alcohol 374, obtained by base-hydrolysis of the acetate 311 (3.4.3.), with Jones-reagent yielded the ketone 375. Unsubstituted 2,8-dioxa-homotwistbren-dane 377) was prepared by converting the ketone 375 to its thioketal 376, which on reductive desulfuration with raney-nickel gave 377. The enolacetate 378 was available by reaction of the ketone 375 with triphenylethylUthium as base followed by addition of acetic anhydride. Under acidic conditions only decomposition could be observed and with pyridine as base no reaction took place. 

Oxidative coupling between pyridine A-oxides (and analogues) and A-substituted indoles via twofold C-H bond activation was achieved in up to 88% yield with high selectivity using Ag2C03 as the oxidant and Pd(OAc)2 as the catalyst in the presence of DMF and pyridine as base and tetrbutylammonium bromide as additive. ... 

Mo(CO)6 has also been used in other types of microwave-promoted carbonylative chemistry. In 2005, Larhed and coworkers presented a carbonylative cyclization protocol whereby ortho-bromo- and ortho-chlorostyrenes were converted into indan-1-ones [21]. Optimized reaction conditions for o-Br-styrenes involved Pd(OAc)2 and 2 as catalytic system with Mo(CO)6 as CO source, n-Bu4NCl as additive and pyridine as base in 1,4-dioxane. Microwave-heating at 150 °C for 30 min provided indanones in 59-82% yield (Scheme 4.5) [21]. 

Evans has developed a direct synthesis of diaiyl ethers while investigating the coupling of functionalized phenolic tyrosine derivatives 96 and 97 [64]. The desired diaryl ethers were obtained in good to excellent yields with pyridine as base and no observed racemization. The thyroxine intermediate 98 was obtained in 81% yield under these conditions using a mixture of pyridine/EtjN (1 1) (5 equiv) as a base (Scheme 3.43). 

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