1.1- Dichloro-l-alkenes

In the reaction of the 1,1-dichloro-l-alkene 611 with phenylzinc chloride, only monoarylation takes place regioselectively to give the (Z)-l-chloro-l-phe-nylalkene 612[468,474],... 

Coupling of vinyl dichlorides.1 This catalyst effects selective coupling of Grig-nard reagents or organozinc chlorides with only one of the chlorine atoms of 1,1-dichloro-l-alkenes (2) to give (Z)-vinyl chlorides (3). The selective coupling involves the chlorine that is trans to the R substituent, probably because of a steric... 

It is noteworthy that 1,1-dichloro-l-alkenes behave differently the reduction is not observed and both chlorine atoms are substituted. Satisfactory yields are obtained by using an excess of Grignard reagent (Scheme 24). 

SCHEME 30. Use of a less polar solvent for higher selectivity in Pd-catalyzed fraas-selective monosubstitution of 1,1-dichloro-l-alkenes... 

The method employing the sequential alkylation and elimination of sulfoxides, reported above, has been successfully applied to the synthesis of dienes (Scheme 86, entry c), aryl alkenes and dienes (Scheme 47), vinyl sulfides, a,3-unsaturated sulfoxides, vinyl fluorides and vinyl chlorides (Scheme 96, entry a), and 1,1-dichloro-l-alkenes (Scheme 96, entry b). ... 

Preparation of alkynes. The 1,1-dichloro-l-alkenes have been converted into 1-alkynes or internal alkynes by treatment with n-butyllithium at -10° to -70°. The resulting lithium alkynides can be hydrolyzed or alkylated (equation 1). 

Dichloro-l-alkenes can also be converted into 1-chloro-1-alkynes by reaction with lithium diethylamide in ether—THF (equation 11) ... 

In contrast to the bromo and iodo analogs, organic chloro compounds are relatively inert toward organolithium reagents. There are only a few classes of chlorinated substrates, notably gm-dichlorocyclopropanes , l,l-dichloro-l-alkenes ° and doubly vicinal oligochlorobenzenes (1,2,3-trichlorobenzene , 1,2,3,4-tetrachlorobenzene , hexachlorobenzene etc.) that are capable of sustaining the halogen/lithium permutation mode. 

The selectivity observed in couplings of 1,1-dihalo-1-alkenes is of interest (Scheme 5.50). 2-Aryl-l,l-dibromoalkenes such as 211 first undergo stereoselective hydrodebromination and subsequent coupHng to afford ( )-alkenes such as 212 if a second equivalent of alkyl Grignard reagent is introduced [141]. Conversely, under almost identical conditions, dichloro analogs such as 213 afford mainly the twofold coupHng products such as 214. Best results for the latter reaction are obtained in THF without NMP [142]. 

Several examples for allylic reagents further substituted by heteroatoms are known. For example, a mixture of the l,l-dichloro-2-alkene and the l,3-dichloro-1-alkene leads to a homogeneous homoallylic alcohol17,18. 

Chemoselective alkenylation in the C-3 position of N-substituted 3,5-dichloropyrazin-2(lH)-ones has been described by Van der Eycken et al. [27]. When a mixture of N-substituted 3,5-dichloropyrazin-2(lH)-one, ethyl acrylate, and NEts in DME, using Pd(OAc)2/DTPB [2-(di-f-butylphosphanyl)bi-phenyl] as a precatalyst, was irradiated for 15 min at 150 °C, the desired /1-fimctionabzed ethyl acrylates could be obtained in moderate yields (Scheme 81). When styrene was used as an alkene, a mixture of E and Z products was isolated. The type of catalyst used proved to be important to avoid competitive Diels-Alder reaction of ethyl acrylate with the hetero-diene system of 3,5-dichloro-l-benzylpyrazin-2(lH)-one. 

The electrochemistry of cobalt-salen complexes in the presence of alkyl halides has been studied thoroughly.252,263-266 The reaction mechanism is similar to that for the nickel complexes, with the intermediate formation of an alkylcobalt(III) complex. Co -salen reacts with 1,8-diiodo-octane to afford an alkyl-bridged bis[Co" (salen)] complex.267 Electrosynthetic applications of the cobalt-salen catalyst are homo- and heterocoupling reactions with mixtures of alkylchlorides and bromides,268 conversion of benzal chloride to stilbene with the intermediate formation of l,2-dichloro-l,2-diphenylethane,269 reductive coupling of bromoalkanes with an activated alkenes,270 or carboxylation of benzylic and allylic chlorides by C02.271,272 Efficient electroreduc-tive dimerization of benzyl bromide to bibenzyl is catalyzed by the dicobalt complex (15).273 The proposed mechanism involves an intermediate bis[alkylcobalt(III)] complex. 

The reactions of l-t-butyl-3-methylallene with several alkenes, e.g. IV-phenylmalei-mide, acrylonitrile and methyl acrylate, afforded exclusively [4 + 2] cycloadducts of 1-t-butyl-l,3-butadiene, which had been formed from l-t-butyl-3-methylallene by a [1,3] sigmatropic rearrangement12. The reaction of l-t-butyl-3-methylallene with 1,1-dichloro-2,2-difluoroethene occurred more rapidly than the hydrogen shift, which allowed the... 

The C = C bond in 3,3,3-trifluoro-2-methylprop-l-eneis readily oxidized in 76 % yield by bubbling the substrate into a cooled solution of hypochlorous acid (Table 6).98 Chlorohydrins together with 1,2-dichloro derivatives arc obtained by oxidation of alkenes with tert-butyl hypochlorite when the reaction is performed in acetic acid instead of water, chlorohydrin acetate is formed (Table 6)."... 

Unlike alkenes, which react reversibly with h, alkynes react in solution irreversibly with I2, forming ( )-l,2-diiodoalkenes.89 The reaction may involve radicals rather than ionic species.90 Ordinary alumina appears to promote the addition, forming electrophilic species.866 The addition of iodine to 1,4-dichloro-but-2-yne is analogous to the addition found with bromine cited above (Scheme 19).28... 

Ethene and ethane account for 80% of the mass of the hydrocarbons identified as products. Trace amounts of methane and acetylene are also produced (Orth and Gillham, 1996). The reduction of PCE forms cis-1,2-dichloroethylene (DCE), frans-l,2-DCE, 1,1-DCE, vinyl chloride, ethylene, dichloroacetylene, acetylene, ethene, ethane, chloroacetylene, methane, and several alkenes ranging from C3 to C6. The trace amounts of dichloro-ethylene and vinyl chloride formed during the reduction of PCE and TCE are further reduced (Burris et al., 1995). Reaction rates vary with substrate, chemical, and microbiological conditions. Selected f1/2 values are provided in Table 13.3. 

IZV118) and the formation of (31) is analogous to the reaction (197)->(98) via a four-membered 1,2-oxathietane 2,2-dioxide intermediate. Subsequent products derived from (31) by electrophilic addition reactions at the alkenic double bond have been described in Section 4.33.3.2.2 and the synthesis of 4,5-dichloro-l,3,2-dioxathiolane 2,2-dioxide (154) by chlorination of ethylene sulfate (18) is discussed in Section 4.33.3.5. Cyclic sulfites, on the other hand, cannot be halogenated without ring opening (cfSection 4.33.3.2.4). 

The second problem in the addition of 1,1-dichlorodifluoroethylene to 1,3-butadiene is regiospecificity. Carbon 1 of 1,3-butadiene may become attached either to the carbon holding two chlorines or to the carbon with two fluorines. The cycloaddition of fluorinated alkenes is usually not a concerted four-center reaction in which the bonds are formed simultaneously or nearly so. Instead, the reaction is a stepwise biradical process in which the first step is formation of a free-radical intermediate with a single electron at that end of the double bond that can better accomodate it. That happens at the carbon linked to two chlorine atoms. Thus, a biradical is formed that cyclizes to form 2,2-dichloro-l,l-difluoro-3-vinylcyclobutane M [118, 119, 720]. 

An example of the reaction of an alkene with 1,1-dichloroethene in anhydrous hydrogen fluoride is the fiuoroalkylation of cyclohexene to yield l,l-dichloro-2-cyclohexyl-l-fluoroethane. ... 

A mixture of dialkyl phosphonate 8 (1.14 mol) and l,2-dichloro-l,2-difluoroethene (0.38 mol) was sealed into a 300-mL Pyrex tube. The reaction was irradiated with y-rays from a Co source for a period of 230 h at I t (total dosage 16 x lO r.). Distillation of the irradiation products under reduced pressure, after removal of unreacted alkene and dialkyl phosphonate. gave the dialkyl l,2-dichloro-l,2-difluoroethylphos-... 

Antimony(V) chloride (SbQj) and molybdenum(V) chloride (MoCls) can react spontaneously with alkenes to give predominantly the corresponding c/s-1,2-dichlorides (equation 11). The reaction probably proceeds through a successive insertion and reductive elimination sequence. The chlorination of butadiene with SbCls and copper(II) chloride results preferentially in the formation of (Z)- and ( )-1,4-dichloro adducts, while the reaction with chlorine gives an 1 1 mixture of 1,2- and 1,4-adducts, as shown in Table 2 and equation (12). The formation of (Z)-l,4-dichloro-2-butene may be ascribed to a transition state as shown in Scheme 3. 

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