Lead methoxide

Insertion into a Pb-OR bond is observed in the reaction of triphenyl or tributyl lead methoxide with a-naphthyl isocyanate however, trimeyhyl lead methoxide causes trimerization of the isocyanates. Careful addition of cyclohexyl- or phenyl isocyanate to tributyllead-A -diethylamine affords the insertion product 305. Reverse addition leads to trimerization. 

Trimethyl-lead methoxide (CH3)3PbOCH3 is polymericio, as shown in Fig. 6. The properties of the lead-oxygen bond in the organolead alkoxides and the organolead oxides... 

Electron-deficient alkenes add stereospecifically to 4-hydroxy-THISs with formation of endo-cycloadducts. Only with methylvinyl-ketone considerable amounts of the exo isomer are produced (Scheme 8) (16). The adducts (6) may extrude hydrogen sulfide on heating with methoxide producing 2-pyridones. The base is unnecessary with fumaronitrile adducts. The alternative elimination of isocyanate Or sulfur may be controlled using 7 as the dipolarenOphile. The cycloaddition produces two products, 8a (R = H, R = COOMe) and 8b (R = COOMe, R =H) (Scheme 9) (17). Pyrolysis of 8b leads to extrusion of furan and isocyanate to give a thiophene. The alternative S-elimi-nation can be effected by oxidation of the adduct and subsequent pyrolysis. 

If the reactions are carried out using a concentration of CHsO slightly less than that of halogenothiazole, the reaction almost quantitatively yields the 2-methoxy-5-nitrothiazole. The reaction of methoxide ion in excess with regard to 2-haiogeno-5-nitrothiazole, previously reported as leading to a mixture of unidentified products together with the expected 2-methoxy-5-nitrothiazole in low yields (97), can be explained on the basis of Scheme 14. 

Comparison of the data for methoxide with those for t-butoxide in Table 6.4 illustrates a second general trend Stronger bases favor formation of the less substituted alkene. " A stronger base leads to an increase in the carbanion character at the transition state and thus shifts the transition state in the Elcb direction. A linear correlation between the strength of the base and the difference in AG for the formation of 1-butene versus 2-butene has been established. Some of the data are given in Table 6.5. 

Treatment of l,2-difluoro-3,5-dinitrobenzene with methoxide leads to a single isomer of fluorodinitroanisole. Obtain the energies of the possible Meisenheimer complexes and predict the structure of the product. Is this outcome consistent with the previously-established directing effect of the nitro group ... 

Pyridine and dimethyl acetylenedicarboxylate in methanol yield - a mixture of (33) and (34). It is tempting to assume that a zwitterion (30) is first formed and that this then adds a proton followed by a methoxide ion (Michael addition) under the influence of both the positive charge on the ring and the assisting ester group. The resulting structure (31) could then add another molecule of the ester and cyclize, as indicated, to (32). Subsequent aromatization accompanied by loss of one, or the other, substituent at position 3 would lead to the two products, (33) and (34), actually isolated. 

The question of the occurrence of cine or aryne substitution in some of these reactions has been raised but not answered adequately. The normal product, 2-methoxynaphthalene was shown to be formed from 2-chloronaphthalene and methoxide ion, and the normal 6- and 8-piperidinoquinolines were proved to be products of piperidino-debromination of 6- and 8-bromoquinolines, all in unspecified yield. More highly activated compounds were then assumed not to react via the aryne mechanism. Even if the major product had been characterized, the occurrence of a substantial or predominant amount of aryne reaction may escape notice when strong orientation or steric effects lead to formation of the normal displacement product from the aryne. A substantial amoimt of concurrent aryne reaction may also escape detection if it yields an amount of cine-substituted material easily removed in purification or if the entire reaction mixture is not chromatographed Kauffman and Boettcher have demonstrated that activated compounds such as 4-chloropyridine do indeed react partially via the aryne mechanism (Section I,C,1). 

Derivatives of 3-oxo-l,2,4-triazine 1-oxide undergo alkylation with various alkylating agents. Thus the reaction of 3-methoxy-l,2,4-triazine 1-oxide 20 with 2,3,5-tii-(9-benzoyl-/3-D-ribofuranosyl bromide, followed by the removal of the benzoyl protection with sodium methoxide, leads to an abnormal nucleoside 4-(/3-D-iibofuranosyl)-l,2,4-triazin-3(4//)-one 1-oxide 21 (73JOC3277). 

Reduction of the imine with sodium borohydride leads to an intermediate amino-ester that cyclizes spontaneously to the <5-lactam function. Solvolysis of the acetyl group with methoxide followed by acylation of the hydroxyl group thus liberated with trimethoxybenzoyl chloride leads to 38. Bischler-Napieralski cyclodehydration (phosphorus oxychloride) effects closure of the remaining ring. Reduction of the imine thus formed with sodium borohydride gives 39. This, it should be noted, leads to the... 

An alternate scheme for preparing these compounds starts with a prefabricated pyrimidone ring. Aldol condensation of that compound (95), which contains an eneamide function, with pyridine-3-aldehyde (80), gives the product 96. Catalytic hydrogenation gives the product of 1,4 reduction. The resulting pyrimidinedione, of course exists in the usual tautomeric keto (97a) and enol (97b) forms. Reaction with phosphorus oxyxchloride leads to the chloro derivative 98. Displacement with methoxide gives 99. Reaction of this last intermediate with the furylalkylamine derivative 92 leads to the H-2 blocker lupitidine (100) [22]. 

Deoxy-D-jcylo hexose 6-(dihydrogen phosphate) (21) has also been synthesized (2) the reaction sequence makes use of 3-deoxy l 2,5 6-di-O-isopropylidene D-galactofuranose (16), a compound that can be easily prepared from D-glucose (2, 60). The mono-isopropylidene derivative (17) formed by partial hydrolysis of the di-ketal is converted into the 6-tosylate (18) by reaction with one molar equivalent of p-toluenesulfonyl chloride. From this the epoxide (19) is formed by reaction with sodium methoxide. Treatment of the anhydro sugar with an aqueous solution of disodium hydrogen phosphate (26) leads to the 6-phosphate (20)... 

The 7-bromo-5-(2-pyridyl)diazepinone 18 reacts with lead(IV) acetate to yield the 3-acetoxy derivative 19, which is converted into the 3-hydroxy compound 20 by the action of sodium methoxide, followed by water.201... 

Reversible additions of sodium methoxide to certain 2,4,6-triarylsele-nopyrylium salts were reported to lead to unstable 2-methoxy-2//-selenopyran intermediates, which could be reconverted into the starting... 

Large concentrations of halide ions, preferably iodide, favour the formation of /ra/i5-stilbene from benzaldehyde and benzyltriphenylphosphonium halides in methanol with methoxide as base, whereas large concentrations of methoxide ions slightly favour formation of the m-isomer. These effects have been explained by the preferential solvation of P+ by halide ions, leading to greater reversibility of betaine formation. Methoxide ions, on the other hand, are preferentially solvated by methanol. 

The crude product of reaction of methanol and carbon monoxide at 100°C/70 bar in presence of 0.5% of sodium methoxide was discharged after cooling into a storage bottle, which burst 4 h later. This was attributed to extreme instability of the ester in presence of the base, leading to the reverse reaction with vigorous evolution of carbon monoxide. Immediate neutralisation of the reaction mixture would prevent the decomposition, which also occurs with ethyl formate and base. See Other GAS EVOLUTION INCIDENTS... 

Tetranitro derivative 90 (z-TACOT Section 12.10.15.5) treated with methanolic sodium methoxide at ambient temperature does not lead to simple product of nucleophilic substitution of a nitro group but provides compound 92. Its formation can be rationalized by introduction of the methoxy group into the 1-position, followed by scission of the remote triazole ring of 91 to give the final product. Compound 90 subjected to the vicarious nucleophilic substitution (VNS) conditions using either hydroxylamine or trimethylhydrazinium iodide gives a very insoluble red solid, which was identified as l,3,7,9-tetraamino-2,4,8,10-tetranitrobenzotriazolo[2,l- ]benzotriazole 93 (Scheme 5) <1998JOC3352>. 

PMMA can exist in two simple stereoregular forms, isotactic and syndiotactic, but commercially available samples—prepared via free-radical initiators—tend to have tacticities lying in the range 60-70% syndiotactic triad content, the exact content depending upon the reaction temperature.426 Several terminating side reactions have been identified, the most important of which is intramolecular cyclization leading to methoxide formation, as shown in Scheme 5.427... 

The cyclizations to obtain cyclic thioureas have been performed using thiocarbonyldiimidazole.232 Reaction of methyl acetoacetate, thiourea and an aliphatic aldehyde in the presence of the zinc iodide (Znl2) was studied. Under the normal pressure, reaction has not been occurred whereas at high pressure (300 MPa) conditions 3,4-dihydropyrimidine-2-thione was obtained only in 10% yield.233 The same one-pot three-component cyclocondensation reaction in the presence of iodide (I2) provides a variety of 3,4-dihydropyrimi-dine-2-thione in high yields.234 Condensation reaction of thioureas with a,p-unsaturated ketones in the presence of the sodium methoxide in methanol affords 3,4-dihydropyrimidine-2-thione derivatives.235,236 Acylation of N,N -disubstituted thioureas with methyl malonyl chloride followed by base-catalysed cyclization leads in the formation of l,3-disubstituted-2-thiobarbituric acids (Scheme 78).237... 

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