Pyridines equation

Another group of Japanese workers91 found that the sulphoxonium salt, 7, was reducible to sulphoxides with either alkyllithiums or lithium dialkylcuprates, the exact reaction pathway being complicated by halide ions originating from the preparation of the metal alkyls. However, good yields of methyl phenyl sulphoxide were obtained by reduction of 7 with sulphur dioxide or a thiol in pyridine (equation 37). 

As a continuation to the studies by Darwish and Braverman on the [2,3]-sigmatropic rearrangement of allylic sulfinates to sulfones, and in view of its remarkable facility and stereospecificity (see Chapter 13), Braverman and Stabinsky investigated the predictable analogous rearrangement of allylic sulfenates to sulfoxides, namely the reverse rearrangement of that attempted by Cope and coworkers . These authors initiated their studies by the preparation of the claimed allyl trichloromethanesulfenate using the method of Sosnovsky . This method involves the reaction between trichloro-methanesulfenyl chloride and allyl alcohol in ether at 0 °C, in the presence of pyridine (equation 6). 

Mercuration reactions provide a convenient approach to a broad range of arylmercury derivatives.82,83 This approach has been applied to a number of substrates, including phenols, indoles, phenylpyridines, and fV-arylamides.83 The products of these reactions as well as their conditions are summarized in Table 1.84 91 Other examples of such reactions include the mercuration of 2-(2 -naphthyl)pyridine (Equation (251)92 and terephthaldehyde (Equation (26))93 with Hg(OCOCF3)2 and Hg(C104)2, which afford 72 and 73, respectively. 

Treatment of the iminoacetate 152 with 4-chlorobenzoyl chloride in the presence of a base gave the desired ethyl 5-(4-chlorophenyl)-l-(2,4-dichlorophenyl)-17/-l,2,4-triazolecarboxylate 153 and the uncyclised ethyl 2-(4-chlorobenz-amido)-2-(2-(2,4-dichlorophenyl)hydrazinyl)acetate 154 in 36% and 6% yield, respectively. The undesired compound 154 was subsequently converted to 1,2,4-triazole 153 in 93% yield by further treatment with pyridine (Equation 47) <2006EJM114>. 

They determined the activation parameters for this reaction in benzene and in benzene containing pyridine (equation 120). 

The direct carbonylation of heterocycles with CO and olefins proceeds efficiently. The reaction of pyridine, CO, and 1-hexene in the presence of Ru3(CO)12 at 150 °C gives a-acylated pyridines (Equation (84)).111,llla A number of olefins including ethene and 1-eicosene can be used in this carbonylation reaction. 

Cycloadditions to a cyano group are comparatively rare. The high-temperature reactions of 1,3-dienes, e.g. butadiene, isoprene and 2-chloro-l,3-butadiene, with dicyanogen, propionitrile or benzonitrile result in formation of pyridines (equation 80)70. Sulfonyl cyanides 147, obtained by the action of cyanogen chloride on sodium salts of sulfinic acids, add to dienes to give dihydropyridines 148, which are transformed into pyridines 149 by oxidation (equation 81)71. 

Fluorinated alkyl cyanides, such as trifluoroacetonitrile, pentafluoropropionitrile, per-fluorobutyronitrile and chlorodifluoroacetonitrile, react with butadiene in the gas phase at 350-400 °C to afford pyridines in high yields (equation 82)72. The push-pull diene 150 and electron-rich cyanides (acetonitrile or acrylonitrile) furnish pyridines (equation 83)73. 

A peri-fused system can be synthesized by diaryl copper-catalyzed ether coupling accomplished utilizing (CuOTf)2 PhMe in pyridine (Equation (21) (2004JOC4527)). This protocol produces several annulated ring systems and gives... 

Yudin and Sharpless reported on the utilization of much cheaper, readily available inorganic Re catalysts [Re207, ReOsfOH), ReOs (0.5-1 mol%)] in combination with bis(trimethylsilyl) peroxide as oxidant and 0.5-1 mol% of pyridine (equation 52) . In this oxidation process high epoxide yields (78-96%) were obtained using CH2CI2 or THF as solvent. Traces of water or other protic species have been found to be essential for rapid turnover and accelerate the reaction. 

Bis(alkylperoxy)diorganosilanes 14 were prepared by the reaction of alkylperoxy diorganochlorosilane with alkyl hydroperoxides in the presence of ammonia or pyridine (equation 20). 

Organotris(alkylhydroperoxy)silanes 16 are synthesized from the reaction of organ-otrichlorosilane with aUcyl hydroperoxides in the presence of pyridine (equation 22). ... 

The reaction of N,N- dimethylaniline with pyridine (equation 55) should also be considered in this category. Enamines usually attack acylated N- oxides at position 2 unless it is blocked, as in 2-methylquinoline 1-oxide, when attack takes place at C-4. Methyl /3-aminocrotonate attacks quinoline and isoquinoline AT-oxides at the position a to the N- oxide function in the presence of tosyl chloride (78JHC1425). However, pyridine and 2-methylpyridine 1-oxides react at the 4-position (equation 142). A low yield of by-product (242) is formed in each case, probably as a result of self-condensation of methyl /3-aminocrotonate. 4-Hydroxyquinoline 1-oxide is exceptional in that it reacts with an enamine in the presence of tosyl chloride at the /3-position (Scheme 170) (B-71MI20500). 5-Amino-3-methylisoxazole reacts with quinoline 1-oxide at the a-position, and the product can be degraded, to afford ultimately 2-methylquinoline (Scheme 171) (78CPB2759). 

A cyclization of enecarbamates leads to the synthesis of pyrrolo[2,3-f]pyridines (Equation 40) <2005TL8877>. The reaction is catalyzed by a copper(l) iodide/L-proline catalyst system. 

Cyanopyridine-4-carboxylate salts can be reduced to give dihydrofuro[3,4-f]pyridines (Equation 51) <2005RJ0279>. Under acidic conditions, the imine fragment can be hydrolyzed to generate lactone product. 

Fused pyridazines, such as 3, that have a chloro substituent a to the nitrogen in the pyridazine ring react with electron-rich ynamines in a reaction sequence including an inverse electron demand Diels-Alder process to give the corresponding pentasubstituted pyridines (Equation 2) <1994CPB2219>. Another isomer of the pyrrolopyridazine as well as a furopyridazine behaved similarly <1994CPB2219>. 

Cyclization of 6-acetylenic derivatives constitutes yet another approach to pyrrolo[3,2-.7 pyrimidines. A series of 6-substituted acetylenes 209, prepared by alkynylation of the chloropyrimidine, undergo cyclization to the A -oxides 210 when heated briefly in pyridine (Equation 72) <2003SL1151, 2004CHE1335>. 

Table 22 Nucleophilic substitution of isoxazolo[5,4-fa]pyridines (Equation 24) <2003S2518>...

Table 23 N-Alkylation of oxazolo[4,5-b]pyridines (Equation 27) <1996TL2409> R Yield (%)...

Table 24 Michael condensation of oxazolo[4,5-fa]pyridines (Equation 28) <1996TL2409>...

A catalytic Fe(lll)/Fe(ll) redox cycling approach to imidazopyridines has also been reported for the synthesis of imidazo[4,5-f]pyridines (Equations 41 and 42) <2000S1380>. 

Pyrazolo[3,4-. ]pyridines have also been formed by reaction of the appropriate chloronitrile pyridine (Equation 50) <2002BML2925>. Pyrazolo[3,4-. ]pyridines can be prepared by oxidative cyclization with PIFA (Equation 51 Table 27) <1997SC2217>. 

Table 30 Synthesis of a wide variety of pyrazoio[3,4-fa]pyridines (Equation 54) <2006301549>...

Table 31 Fluorinated pyrazolo[3,4-b]pyridines (Equation 55) <2004SC4359>...

The triphenylphosphine-hexachloroethane system was also used to form oxazolo[5,4-3]pyridines (Equation 62). The reaction conditions tolerated a wide variety of substituents in the 2-position, and even a sterically bulky group did not decrease dramatically the yield of desired products <2005TL9001>. 

Table 34 Synthesis of pyrazolo[4,3-c]pyridines (Equation 81) <2004T933>...

Dibenzothienobisbenzothiophene has been synthesized by the intramolecular cyclization of aromatic methyl sulfoxides under acid conditions followed by demethylation <1999JMC2095>. Thus, treatment of the corresponding sulfoxide with trifluoromethanesulfonic acid gives the cyclized product which is demethylated in refluxing pyridine (Equation 73). 

The nonclassical heterocycles 17 and 54 are prepared in high yields by the reaction of diamine 204 with thionyl chloride or A -thionylaniline and trimethysilyl chloride in pyridine (Equation 135). The corresponding selenium analogues were prepared by reaction of 193 with selenium dioxide (Table 15) <1995JA6791, 1997T10169>. 

Under thermal conditions bicyclic azetines undergo facile valence bond tautomerization. Typically, l-azabicyclo[2.2.0]hexadienes give pyridines (equation 16) (76CPB2219), 1,2-diazabicyclo[3.2.0]heptadiene (126) gives diazepine (127) (77CJC56) and 2-... 

Thus it was shown that while the iodides were reduced, the reactions followed an entirely different path than those of the chlorides and bromides. These reactions may be described by Equation 5. However, the reactions may proceed through initial coordination of pyridine (Equation 6), followed by dissociation to yield the final products (Equation 7). 

Cyclization of the free acids in acetic anhydride may lead to the decarboxylated 3-acetoxy derivative (Section 3.15.2.2.3). Several 3-hydroxybenzo[6]thiophenes were obtained in excellent yield by the interaction of phenylsulfonylbenzisothiazolone with substances containing a reactive methylene group in the presence of pyridine (equation... 

The displacement of halogen with a copper(I) acetylide and subsequent or synchronous copper catalyzed addition of a neighboring nucleophilic substituent to the triple bond (equation 2) constitutes a versatile synthesis of heterocycles. This reaction has been utilized both for the synthesis of furo[3,2-c]pyridines (equation 3) and furo[3,2-6]pyridines (equation 4) (68JHC227, 72MI31700>. 

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