Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Carboxylic acids dichloromethyl esters

To that end they converted dichloroacetonitrile to 2-(dichloromethyl)-4-oxazo-line carboxylic acid methyl ester 355 in 88% yield. Treatment of 355 with one equivalent of sodium methoxide produced 356 via an internal transfer of oxidation state through a molecular framework. The synthesis was completed by acid-catalyzed elimination of methanol to afford 357 in 48% overall yield from dichloroacetonitrile. [Pg.77]

If carboxylic acid esters are readily available, they provide a convenient basis for the preparation of acid halides. Modified phosphorus halides, like 2,2,2-trichloro-l,3,2-benzodioxaphosphole can be applied successfully. This reagent forms first a 1,1-dichloroalkyl ether, which decomposes to the acid chloride (equation 16). The reaction conditions are rather drastic. For instance -butyl benzoate has to be heated for 4 h at 180 °C in order to get a 90% yield of benzoyl chloride. The only stable and isolable 1,1-dichloro ether is a,a-dichloromethyl methyl ether, which, as described above, is used as a mild reagent for the conversion of carboxylic acids to their chlorides. Similarly severe conditions are required if the chlorine or bromine adduct of triphenylphosphine is selected. This reaction may be catalyzed by BF3. It has been applied successfully to unsaturated esters and to the cleavage of lactones. [Pg.307]

Reaction with carboxylic adds. A surprising finding is that phenyl(bromodichIoro-methyl)mercury reacts with carboxylic acids in benzene at 60-80° in about 45 min. to give dichloromethyl esters in high yield phenylmercuric bromide is produced in virtually quantitative yield ... [Pg.1160]

Indeed, the reaction of an equimolar quantity of bromodichloromethyl(phenyl)mercury with alk-2-enoic acids affords the dichloromethyl esters. Dichlorocyclopropanation is only possible if a second mole of carbene source is used (see Houben-Weyl, Vol. 4/3, pp 178-179). Competition between acetic acid and cyclohexene for dichlorocarbene indicates that the acid is considerably more reactive.Furthermore, dichloromethyl 2,2-dichlorocyclopropane-carboxylates cannot be hydrolyzed to the corresponding acids. To avoid all of these difficulties, addition of dichlorocarbene, generated under nonhydrolytic conditions using dichloro-halomethyl(phenyl)mercury, to the bromides of alk-2-enoic acids is possible. [Pg.677]

Disubstituted pyrroles lacking substituents at the 3- and S-positions are often required in porphyrin synthesis, and these can now be prepared from pyrrole itself. Thus, trichloroacetylation or trifluoroacetylation of pyrrole affords the 2-trihaloacetylpyrrole 8, which can be converted into the corresponding esters 9, carboxylic acids, or amides. The amides have been acetylated, or formylated, at the 4-position specifically, and the resulting acyl pyrroles (10) have been reduced to the alkyl pyrroles (11). This general procedure has now been improved by direct Friedel-Crafts formylation of the trichloroacetylpyrrole (8a) with dichloromethyl methyl ether (aluminium chloride) to the diacylpyrroles... [Pg.241]

Asymmetric boronic esters synthesized by hydroboration chemistry have been converted into asymmetric carboxylic acid derivatives having carboxyl carbon in place of the boron atom via homologation with (dichloromethyl)lithium and oxidation [7]. This sequence is relatively inefficient because of the several steps required. If the asymmetric boronic ester is generated via catalytic hydroboration with catecholbo-rane, the homologation process is a more efficient way of introducing the carboxyl carbon [72],... [Pg.333]


See other pages where Carboxylic acids dichloromethyl esters is mentioned: [Pg.124]    [Pg.249]   


SEARCH



1,1 -dichloromethyl

© 2024 chempedia.info