Dichlorocarbene reaction with olefins

Contents Introduction and Principles. - The Reaction of Dichlorocarbene With Olefins. - Reactions of Dichlorocarbene With Non-Olefinic Substrates. -Dibromocarbene and Other Carbenes. - Synthesis of Ethers. - Synthesis of Esters. - Reactions of Cyanide Ion. - Reactions of Superoxide Ions. - Reactions of Other Nucleophiles. - Alkylation Reactions. - Oxidation Reactions. - Reduction Techniques. - Preparation and Reactions of Sulfur Containing Substrates. -Ylids. - Altered Reactivity. - Addendum Recent Developments in Phase Transfer Catalysis. 

Dichlorocarbene is the reactive intermediate formed by the reaction of alkali on chloroform, and typically it adds to olefins to give 1,1-dichlorocyclo-propanes. The PTC procedure for the generation of dichlorocarbene is particularly useful and is illustrated by its reaction with cyclohexene to form (38) (Expt 7.15). The mechanism is formulated below and probably involves the reaction of the quaternary ammonium hydroxide with chloroform at the phase boundary, and dissolution into the organic phase of the quaternary ammonium derivative of the trichloromethyl anion (41). This species breaks down to form dichlorocarbene and the quaternary ammonium chloride. The latter returns to the aqueous phase to maintain the cycle of events, while the dichlorocarbene reacts rapidly with the cyclohexene in the organic phase. 

Butatrienes. Olefins can be converted into butatricncs by reaction with dichlorocarbene followed by treatment with potas.sium r-butoxide in t-butanol (or sodium meth-oxide in DMSO). Yields are in the range 50 90%. 

Kinetic studies of the reaction of phenyl(bromodichloromethyl)mercury with olefins show that dichlorocarbene is liberated as a free species. Moreover, the fact that the reaction is insensitive to the effect of substituents in the phenyl group suggests that the extrusion process proceeds in a concerted process through a cyclic transition state, 5a or 5b.7c... 

Kobrich0 has presented evidence that the reaction of trichloromethyllithium with olefins is stereospecific and that it probably does not proceed through prior decomposition to dichlorocarbene. He suggests a cyclic transition state in which lithium chloride is present. Tribromomethyllithium has been prepared in high yield from the reaction of tetrabromomethane and phenyllithium or n-butyllithium.7... 

Precursor of dichlorocarbene. Treatment of chloral with potassium /-butoxide at about 0° leads to dichlorocarbene, as shown by the reaction with an olefin.1... 

The effect of substituents other than alkyl on the reactivity of olefins has received little attention so far. The variation with n in the compounds (CH j)3Si(CH2) CH=CH2 of the dipole moment , the rates of reaction with ethyl diazoacetate (CuSO -catalyzed) , and the rates of dichlorocarbene addition are listed in Table 22. The maximum at = 1 reflects the opposite effects of bonding from the double bond to silicon and of the inductive effect... 

The reaction of carbenes with olefins to form cyclopropyl derivatives has been used to modify elastomers. Pinazzi and Levesque and Berentsvich et al. found that carbene addition had a significant influence on the properties of polydienes. Thermogravimetric analysis (TGA), flammability and oil resistance in NR and dichlorocarbene modified styrene butadiene rubber (DCSBR) blends were investigated by thermogravimetrie analysis as a funetion of different composition. The TGA plots confirmed the better thermal stability and flame resistance of DCSBR as well as its blends with NR. The amount of DCSBR in the blend significantly affected the properties of blends. 

Despite the many advantages of the phase transfer method for generating dichlorocarbene, it should be noted that the reactive species arises from the trichloromethide anion as it does in most other methods. Because of this, attempted reactions with electron poor olefins will yield products arising from Michael addition of ClaC" to the olefin instead of, or in addition to, cyclopropanation products. The thermal decomposition of trihalomethyl metal compounds remains the unique method for generating dihalocarbenes without prior formation of a trihalomethyl anion [8]. 

The Reaction of Dichlorocarbene With Olefins Table 2.1 (continued)... 

Dichlorocarbene generated in a two-phase system in the presence of a chiral amine catalyst, reacts with olefins to afford dichlorocyclopropanation products having small optical rotations. The reaction is discussed in terms of steric interactions in the transition state and is analogous to those discussed in section 2.2 and equations 2.9—2.11. 

Direct evidence for the existence of dichlorocarbene, by trapping with a suitable substrate, was obtained by Doering and Hoffmann in 1954. Dichlorocarbene was shown to add in a characteristic manner to the double bond of cyclohexene to give dichloronorcarane (1) in 59% yield similar adducts were obtained with other olefins. Bromo-form imderwent an analogous reaction in the presence of olefins to give... 

The reactions of dichlorocarbene with phosphorus ylides result in the corresponding olefins and phosphines.66-68 In the reaction of dichlorocarbene generated in situ with tributyl- and triphenylmethylenephosphoranes or triphenylethylidenephosphorane, the olefin yield increases as the nucleo-philicity of phosphorus ylide increases. According to,67 the reaction starts from the electrophilic attack of carbene at the a-C atom of phosphorus ylide. Then the intermediately formed betaine (28) (Scheme 14) decomposes to eliminate the phosphine molecule and form dichloroolefin (29). 

The generation of dichlorocarbene for addition to olefins has been realized by the use of chloroform and alkali metal alk-oxides4 6 (preferably potassium feri-butoxide), sodium trichloro-acetate,6 butyllithium and bromotrichloromethane,7 and the reaction of an ester of trichloracetic acid with an alkali metal alkoxide.2,8 The latter method, which is here illustrated by the preparation of 2-oxa-7,7-dichloronorcarane, generally gives higher yields of adducts. 

Systematic studies of the dicyclopropanation of olefinic sugars have been published [194], Dichlorocarbene, generated under phase-transfer catalysis reacts with 2,3-unsaturated pyranosides, such as 161 to yield a single isomer of the expected cyclopropane 162 (Scheme 55). A typical procedure is given in Section IE. The reaction is also possible with an enol... 

You will become familiar with selected cycloadditions that lead to four-, five-, or six-membered rings in Chapter 12. Two more cycloadditions, which are also oxidations, will be examined in Chapter 14, which deals with oxidations and reductions the ozonol-ysis reaction can be found in Section 14.3.2 (as well as in Section 12.5.5) and the cis-vic dihydroxylation with 0s04 can be found in Section 14.3.2. Here we discuss only the addition of dichlorocarbene to olefins as an example of a cis addition of the cycloaddition type (Figure 3.11). 

Polymerization. Monomers. The cyclopropane type monomers are prepared either by addition of the dichlorocarbene or by the Simmons-Smith reaction on the corresponding olefins. Most of these compounds have been described. Spiropentane is prepared by the Applequist method (I, 2), by the reaction of zinc with C(CH2Br)4 in alcohol in the presence of ethylenediaminetetraacetic acid (EDTA). This hydrocarbon is purified until a single NMR signal is obtained at t = 9.28. 

Dichlorocarbene. Polish chemists have reported a new method for generation of dichlorocarbene (or a carbenoid species) it involves the reaction of an olefin with chloroform in the presence of a 50 % aqueous NaOH solution and a catalytic amount of benzyl-triethylammonium chloride. For example, dichloronorcarane was obtained from cyclohexene in this way in 72% yield. In the absence of the catalyst, a yield of only 0.5% has been reported.2... 

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 ... 

Dichlorocarbene. This silane decomposes in the vapor phase at 120-140° to liberate dichlorocarbene and SiF3Cl. Added olefins are converted into gem-dichlorocyclopropanes in 85-95% yields. The reaction is stereospecific with cis- and tra/is-2-butene. ... 

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