1,1 -Dichloro-1 -alkenes

SCHEME 46. Comparison of the Negishi and Sonogashira reations in the Pd-catalyzed alkynylation of 1,1-dichloro-1-alkenes... 

A number of 3,5-dihalogenoalkenyl-l,2,4-thiadiazoles (346) have been obtained204 by treatment of the dimercapto compound with dichloro-alkenes (e.g. 2,3-dichloropropene) in aqueous sodium hydroxide. The reaction with chloroacetic acid yields l,2,4-thiadiazolyl-3,5-di(thio-glycollie) acid,144 which forms salts and may be esterified in the usual way. 

Calculations at the B3LYP and MP2 levels of theory with the 6-31+G basis set were used to model the S 2 reactions of the intermediates formed when alkyllithiums were reacted with several 1,1-dibromo- and 1,1-dichloro-alkenes.118 The calculations showed, correctly, that the most sterically constrained halogen was attacked in the first step of the reaction and that the intramolecular substitution reaction in the second step of the reaction occurred by an SN2 mechanism. 

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],... 

Chlorohydnns and 1,2-dichloro denvatives are obtamed by oxidation of alkenes with fert-butyl hypochlorite when the reaction is performed in acetic acid instead of water, chlorohydrm acetate is formed [Ji] (equation 25)... 

Fluorinated cyclobutanes and cyclobutenes are relatively easy to prepare because of the propensity of many gem-difluoroolefins to thermally cyclodimerize and cycloadd to alkenes and alkynes. Even with dienes, fluoroolefins commonly prefer to form cyclobutane rather than six-membered-ring Diels-Alder adducts. Tetrafluoroethylene, chlorotrifluoroethylene, and l,l-dichloro-2,2-difluoroethyl-ene are especially reactive in this context. Most evidence favors a stepwise diradical or, less often, a dipolar mechanism for [2+2] cycloadditions of fluoroalkenes [S5, (5], although arguments for a symmetry-allowed, concerted [2j-t-2J process persist [87], The scope, characteristic features, and mechanistic studies of fluoroolefin... 

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. 

The injected sulfonyl chlorides decompose instantaneously to give peaks of monochloroalkanes and 1-alkenes from alkanesulfonyl chlorides and dichloro-alkanes, and monochloro- 1-alkenes from monochloroalkane sulfonyl chlorides ... 

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. 

A related cyclization of N-sulfonyl-amino-alkenes and NBS gave the bromo-lactam, " and a dichloro-Af,7/-bisallylamide was converted to a dichloro-lactam with FeCl2. ... 

The thermolysis products of silaazetidines support the formulation of stepwise decomposition to alkene and Cl2Si=NR derivatives [3,4], The silene is not liberated from the silaazetidines when performing thermolysis reactions, but the Si-dichloro substituted silanimine (Cl2Si = N/Bu) is formed. This can be trapped by M SiOMe or Ph2C=NfBu, to give the addition products. 

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. 

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... 

Addition of halocarbons to alkenes in the presence of transition metals is a well-known radical reaction. Weinreb etal. have now reported an intramolecular version leading to cyclic esters or bicyclic lactones. Typical substrates are the a,a-dichloro ester 1 or the a,a-dichloro acid 2, readily available by reaction of ethyl lithiodi-chloroacetate with 5-bromo-l-pentene. When 1 is heated in benzene at 160° with a metal catalyst, mixtures of epimeric ot,w-dichloro esters 3 and 4 are obtained. The ratio and yields of 3 and 4 are dependent on the catalyst and concentration of 1, but 3 and 4 are the major products formed in the presence of Ru(II) and Fe(II) catalysts. In contrast cyclization of 2 under the same conditions gives the bicyclic y-lactone 5 in high yield. 

Boyes and Wild reported the manganese-mediated regioselective chlorination of allenes [14]. For the dichlorination of cyclo-l,2-nonadiene, the dichloride was obtained as the major product whereas the reaction of monosubstituted allene afforded a mixture of regiosomers of the dichlorination products with 2,3-dichloro-1-alkene 12 being the major one. The yield with oxalyl chloride is better than that with TMSC1. 

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... 

Cyclic trithiocarbonates are conveniently prepared by the phase-transfer catalysed reaction of 1,2- and 1,3-dichloro- and dibromoalkanes with sodium trithiocarbonate [47]. Diodoalkanes produce alkenes. 

Chloro(phenylthio)carbene [32] has been produced by the standard phase-transfer catalytic procedure from PhSCHCK and trapped by alkenes (see Section 7.3), although the carbene is also prone to dimerization to give [PhS(Cl)C=C(Cl)SPhj. In a similar manner, phenylthiocarbene has been obtained from PhSCH2Cl [33] and chloro(phenoxy)carbene from dichloro(phenoxy)methane [34]. Reaction of the analogous seleno derivatives produce the conesponding phenylselenocarbenes... 

The inverse-electron-demand Diels-Alder reaction of 3,6-dichloro[l,2,4,5]tetrazine with alkenes and alkynes provides the synthesis of highly functionalized pyridazines. ° Also, the 4 + 2-cycloaddition reactions of the parent [l,2,4,5]tetrazine with donor-substituted alkynes, alkenes, donor-substituted and unsubstituted cycloalkenes, ketene acetals, and aminals have been investigated. ... 

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. 

Dichlorodithionitronium cation, ClSNSCl, adds to alkynes forming cations (87) in 97% yield probably via the intermediate l,3-dichloro-l,3,2-dithiazolinium cations (90) <90CJC852>. Cation Cl2S2N is less reactive than cation S2N it does not add to hexafluoro-2-butyne or MeCN. However, it is more accessible and preferable for preparative purposes. It adds also to alkenes quantitatively giving stable l,3-dichloro-l,3,2-dithiazolinium cations (91) which in turn can add to excess of alkene with loss of chlorine affording bicyclic cations (89) <90CJC852>. Tetrafluoroethene does not react evidently on electronic grounds, tetramethylethene fails to form expected adducts presumably for steric reasons. 

An unusual incorporation of iodine derived from the Na(lO ) used in RuClj/aq. Na(10 )/CCl -CH3CN was noted in the oxidation of the terminal alkene 2-allyl-2,5-dichloro-4-morpholino-cyclopent-4-ene-l,3-dione giving the iodohydrin 5 3,7-dichloro-l-P-hydroxy-3 3-iodomethyl-8-morpholino-2-oxabicyclo[3.3.0]-oct-7-en-6-one and its 3a-epimer. The iodine apparently derives from the formation of or T from the lOj" to which IO is reduced after the RuClj/IO " reaction (Fig. 3.21) [236]. 

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