Methyl-substituted phosphite

These cycloadditions are more sensitive to the quality of the catalyst, the major side reaction being protodesilylation of the allylsilane subunit. Since this can not be measured readily either in the case of the tetrakis(triphenylphosphane)palladium(0) or the palladium acetate/triisopropyl phosphite methods, an improved method for generating the palladium(O) species has been developed22. This involves in situ preparation of tetrakis(triisopropyl phos-phite)palladium(O) by direct reduction of palladium acetate with butyl lithium. This method is illustrated by the addition of the methyl-substituted TMM-Pd complex to eyelopentenone. 

With cyclic phosphites derived from glycols, opening of the ring occurs preferentially for unsubstituted or methyl-substituted 5-mem-bered rings (A = H or Me) (21,29,32,34,36,230), equation 4. The... 

Electrophilic substitution of the ring hydrogen atom in 1,3,4-oxadiazoles is uncommon. In contrast, several reactions of electrophiles with C-linked substituents of 1,3,4-oxadiazole have been reported. 2,5-Diaryl-l,3,4-oxadiazoles are bromi-nated and nitrated on aryl substituents. Oxidation of 2,5-ditolyl-l,3,4-oxadiazole afforded the corresponding dialdehydes or dicarboxylic acids. 2-Methyl-5-phenyl-l,3,4-oxadiazole treated with butyllithium and then with isoamyl nitrite yielded the oxime of 5-phenyl-l,3,4-oxadiazol-2-carbaldehyde. 2-Chloromethyl-5-phenyl-l,3,4-oxadiazole under the action of sulfur and methyl iodide followed by amines affords the respective thioamides. 2-Chloromethyl-5-methyl-l,3,4-oxadia-zole and triethyl phosphite gave a product, which underwent a Wittig reation with aromatic aldehydes to form alkenes. Alkyl l,3,4-oxadiazole-2-carboxylates undergo typical reactions with ammonia, amines, and hydrazines to afford amides or hydrazides. It has been shown that 5-amino-l,3,4-oxadiazole-2-carboxylic acids and their esters decarboxylate. 

Reaction of the conjugate base of diethyl phosphite with 3-car-boxyethyl-substituted 2,5-halomethylfurans provided interesting products as alternatives to the normally anticipated Michaelis-Becker substitution-type products.452 Rather than simple substitution, overall reduction of the halomethyl linkage(s) to methyl(s) were observed with a Michael-type addition of phosphorus to the 4-position of the ring. 

Benzyl methyl Y-substituted benzyl phosphites (280) react in CCI4 at low temperature (-20 to 40 °C) with r-butyl hypochlorite (279) to give a complex mixture of products. Tetraalkoxyphosphonium chlorides (281 At = YC6H4) are the key intermediates, and it is proposed that they can undergo heterocyclic fragmentation in five different ways (Scheme 30). ... 

The intermediate cyclooctene complex appears to be more reactive with respect to CS coordination and more sensitive to oxidation when the arene ring bears electron-withdrawing groups (e.g., C02CH3). Dicarbonyl(methyl rj6-benzoate)-thiocarbonyl)chromium is air stable in the solid state and reasonably stable in solution.9 The infrared spectrum exhibits metal carbonyl absorptions at 1980 and 1935 cm"1 and a metal thiocarbonyl stretch at 1215 cm"1 (Nujol) (these occur at 1978, 1932, and 1912 cm"1 in CH2C12 solution).10 Irradiation of the compound in the presence of phosphite or phosphine leads to slow substitution of CO by these ligands, whereas the CS ligand remains inert to substitution. The crystal structure has been published."... 

The iV-4-(benzotriazolylmethyl)-tetrahydro-l,4-benzodiazepine 59 reacted smoothly with Grignard reagents in THF to provide convenient access to substituted homologues in good yield (Scheme 25) <2002J(P1)592>. The benzo-triazole moiety can be removed reductively with NaBFLr to provide the simple jV-methyl compound, while reaction with triethyl phosphite and ZnBr2 in dry THF gave the diethylphosphonate derivative. 

When this type of reaction was applied to the preparation of the ester 2, phosphorus trichloride was used as the phosphorus (III) halide. Treatment of this with one mole equivalent of 3,3-dimethoxyprop-l-ene yields mainly the enol ether 4, with smaller amounts of the isomeric a-chloroallyl methyl ether 5. This mixture is not very stable and has to be treated with trimethyl phosphite rapidly, in order to provide 2 in good yield, as shown in Scheme 1. The significance of this sequence is that it reveals that since 2 is the only product, the reactions leading to 2 via 4 must proceed by two allylic inversions, whilst those via 5 involve direct substitution twice at the original acetal carbon. 

Treatment of the conanine (372) with bromine-aqueous sodium carbonate yields192 (100%) the conenium salt (375) which is readily converted into (376) (80%). Compound (376) is also formed starting from (373). When C-20 is substituted by two methyl groups as in (374) the product is (377). The conanine (373) is photo-oxygenated,193 in the presence of methylene blue, to (376). The nitrone (378) is quantitatively deoxygenated by triphenyl phosphite with trimethyl phosphite the reaction is more complex.194... 

The phosphorus activation of alcohols to substitution with inversion of configuration. The reactions are based on the high heat of formation of the P-O bond and the tendency for phosphorus to form multiple bonds with oxygen. For example, treatment of an alcohol with triphenyl phosphite and methyl iodide leads to the corresponding iodo compound (Scheme 2.17). 

The degree of substitution and the structure of the cellulose phosphites were determined by comparing the contents of phosphorus and methoxyl groups in the reaction products. The data (7/) indicate that mainly mixed esters of methyl alcohol and cellulose with phosphorous add form at the first reaction step a longer reaction time results in almost complete replacement of the methoxyl groups according to scheme (b). 

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