Sodium trichloroacetate, dichlorocarbene

If water is not rigorously excluded from sodium trichloroacetate dichlorocarbene synthesis, what side reaction occurs ... 

Dichlorocarbene can be generated by heating sodium trichloroacetate. Propose a mechanism for the reaction, and use curved arrows to indicate the movement of electrons in each step. What relationship does your mechanism bear to the base-induced elimination of HC1 from chloroform ... 

Treatment of benzo[c][l,5]naphthyridine with dichlorocarbene, formed from the thermal decomposition of sodium trichloroacetate, gives the corresponding iV-dichloromethylide, 1,3-dipolar cycloaddition of which with DMAD, with loss of HC1, gives the corresponding pyrrolonaphthyridine 284 (Equation 98) <1995M227>. In the [1,6]- and [1,7]-naphthyridine series, compounds 285 and 286 are obtained by the same route and in the [l,8]naphthyridine series compound 287 is obtained from the parent naphthyridine, dichlorocarbene, and dimethyl maleate followed by oxidation (Equation 99) <1998RJ0712>. 

Chloromethyltriphenyllead compounds, Ph3PbR (R = CC13 or CHC12), have been proposed as products of the decomposition of the triphenyllead chloroacetates in refluxing pyridine on the basis of equivocal spectroscopic data (37). Trichloromethyltriphenyllead was isolated for use as a source of dichlorocarbene from the reaction of triphenyllead chloride and sodium trichloroacetate in dme at 85° C (35) [Eq. (33)]. 

Alternative procedures for the generation of dichlorocarbene and dibromocarbene under phase-transfer catalysed conditions are also available. Where the reactive substrate is labile under basic conditions, the thermal decomposition of solid sodium trichloroacetate or bromoacetate under neutral conditions in an organic solvent is a valuable procedure [10-12], The decarboxylation is aided by the addition of a quaternary ammonium salt, which not only promotes dissolution of the trihaloacetate anion in the organic solvent, but also stabilizes the trihalomethyl anion. Under optimum reaction conditions, only a catalytic amount of the quaternary ammonium salt is required, as a large amount of the catalyst causes the rapid generation of the dichlorocarbene with resultant side reactions. 

Phase-transfer catalysed reaction of dichlorocarbene generated from sodium trichloroacetate... 

Dehydrochlorination of pentachlorocyclopropane, formed from trichloroethylene and sodium trichloroacetate as a source of dichlorocarbene, yields tetrachloro-cyclopropene [150], a particularly versatile reagent for various applications. It is a reasonably reactive dienophile [151], a reagent applicable to heterocyclic synthesis [152], and an electrophile for aromatic substitutions [153] and additions to alkenes [154] in the presence of Lewis acids. 

For example, methyl 3-phenylbicyclofl.l.0]butane-l-carboxylate (11, R1 = Ph R2 = C02Me) was converted to methyl 2,2-dichloro-3-phenylbicyclo[l.l.l]pentane-l-carboxylate (12, R1 = Ph R2 = C02Me) in 46% yield on reaction with dichlorocarbene generated by thermolysis of sodium trichloroacetate. 3,14... 

The dichloromethyl derivative 20 is isolated (10%) from 3,4,5-trimethyI-pyrazole and chloroform in the presence of sodium ethoxide generation of dichlorocarbene by thermolysis of sodium trichloroacetate does not give any 4/Z-pyrazole.30 The same product is formed, in lower yield, using chloroform and base with a phase-transfer catalyst.31... 

The reaction of dihydrobenzothiazepines (1) with dichlorocarbene, generated in situ from chloroform using a phase-transfer catalyst or by thermal decomposition of sodium trichloroacetate, afforded compounds 2 in low yields (18-24%) (Scheme 1). The structure of 2 was postulated on the basis of analytical and spectroscopic data and confirmed by X-ray diffraction (92MI1). 

The problem with many of these reactions is that they require strong bases—either the organometallic compound itself is basic or a base must be used to create the carbanion. Carbenes are so unstable that they must be formed n the presence of the compound they are intended to react with, and this can be a problem if that compound is base-sensitive. For dichlorocarbene, a way round the problem is to make the carbanion by losing CO2 instead of a metal or a proton. Decarboxylation of sodium trichloroacetate is ideal as it happens at about 80 °C in solution. 

In addition to using CHX3 and base to synthesize dihalocarbenes (Section 26.4), dichlorocarbene ( CCl2) can be prepared by heating sodium trichloroacetate. Draw a stepwise mechanism for this reaction. 

There are a dozen or so ways by which dichlorocarbene may be generated. In this experiment thermal decomposition of anhydrous sodium trichloroacetate in an aprotic solvent in the presence of cis,cis-l,5-cy-clooctadiene generates dichlorocarbene to give 5,5,10,10-tetrachloro-tricyclo[7.1.0.0 ]decane (1). 

Thermal Decomposition of Sodium Trichloroacetate Reaction of Dichlorocarbene with 1,5-Cyclooctadiene... 

The thermal decomposition of sodium trichloroacetate initially gives the trichloromethyl anion (Eq. 1). In the presence of a proton-donating solvent (or moisture) this anion gives chloroform in the absence of these reagents the anion decomposes by loss of chloride ion to give dichlorocarbene (Eq. 2). 

Tetrachloroethylene, a nonflammable solvent widely used in the dry cleaning industry, boils at 121°C and is relatively inert toward electrophilic dichlorocarbene. On generation of dichlorocarbene from either chloroform or sodium trichloroacetate in the presence of tetrachloroethylene, the yield of hexachlorocyclopropane (mp 104°C) is only 0.2-10% (W. R. Moore, 1963 E. K. Fields, 1963). The first ideafor simplifying the procedure was... 

Surprisingly, with dichlorocarbene generated by another method (ther-mocatalytic decomposition of sodium trichloroacetate instead of alkaline hydrolysis of chloroform under phase-transfer catalysis conditions) N-(p-R-benzylidene)-feH-butylamines 55 (R = H, Cl) give 3,3-dichloroazetidi-... 

A comparison of olefin reactivities toward CeHjHgCBrCt in benzene at 80° with the reactivities of the same olefins toward sodium trichloroacetate in 1,2-dimethoxy-ethane at 80° established near identity of the relative reactivities toward both reagents, a result which favors the interpretation that both reactions involve free dichlorocarbene as an intermediate. Of practical significance is the fact that yields are consistently higher by the mercurial route. Thus the latter route proved effective as applied to olefins of low reactivity toward dihalocarbenes generated by other procedures. Examples are formulated ... 

To effect addition of dichlorocarbene to trichloroethylene to produce penta-chlorocyclopropane, Tobey and West heated and stirred a mixture of 1,600 g. of commercial sodium trichloroacetate containing 6% of water with 2.5 1. of trichloroethylene under a water take off trap for removal of all water (2 hrs.). Evolution of... 

The addition of dichlorocarbene, generated by thermolysis of sodium trichloroacetate, to 7-methylene- and 7-isopropylidenenorbornenes is preferentially syn selective when the norbor-nene contains electron-withdrawing c /o-substituents. ... 

A mixture of the monoadducts 14 and 15, one of which rearranged, was formed from 1-phenyl-buta-1,2-diene and dichlorocarbene generated from ethyl trichloroacetate/sodium methoxide. Under the conditions of the chloroform/base/phase-transfer catalyst or thermolysis of sodium trichloroacetate methods, dichlorocarbene reacts further with the rearranged product to give 16. ... 

A variety of methods have been tried for the preparation of hexachlorocyclopropane from tetrachloroethene and dichlorocarbene the chloroform/base/phase-transfer catalyst method fails, the chloroform/potassium fert-butoxide and sodium trichloroacetate/heat methods give 0.2 to 1.0% yield, using chloroform/85% solid potassium hydroxide at 100 to 110 °C for ca. 45 minutes the yield is 4.5% and finally the bromodichloromethyl(phenyl)mer-cury/heat method afforded the product in 83% yield. 

Using bromodichloromethyl(phenyl)mercury, vinyl acetate afforded 2-acetoxy-l,l-dichlo-rocyclopropane (1, 85%), dichlorocyclopropanation of other aldehyde enol esters would also be expected. The cyclopropane 1 ( 10%) together with 2-acetoxy-l,l,l-trichloropropane (2,10%) were formed when the dichlorocarbene was generated from sodium trichloroacetate, the chain product 2 results from the reaction of the trichloromethyl anion (for the mechanism, see ref 197). These reactions are described in Houben-Weyl, Vol. 4/3, pp 177-178. Under phase-transfer catalytic conditions (CHClj/base/PTC), with a typical catalyst such as benzyl-triethylammonium chloride, vinyl acetate gave 2 (65%) only (Houben-Weyl, Vol.E19b, ppl550-1551). 

Esters of, y-unsaturated acids did not isomerize to conjugated isomers when they reacted with the dichlorocarbene generated from sodium trichloroacetate, e.g. cyclopropane 13. ... 

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