Alkynes chlorination

Amino alkynes such as 1.172 are usually prepared by reaction of a chlorinated alkyne. such as 6-chloro-l-hexyne and an amine such as dimethylamine. 3 it is also possible to do the amination step after formation of, or incorporation of, the acid moiety, and this generates amino tetrolic acids (4-aminobut-2-ynoic acids). 

The requirement for photoinitiation indicates that a radical-chain mechanism must be involved. Chlorination of 1-pentyne carried out in a gas phase reactor at higher temperatures and with higher chlorine alkyne ratios gives both the trans dichloroalkene and the saturated tetrachloro compound derived from addition of a second mole of chlorine.Fair yields of dichloroalkenes, predominantly the cis dihalide, can be obtained from acetylenes by reaction with antimony penta-chloride... 

NCP) as the source of electrophilic chlorine and DBU as the base, excellent yields of the chlorinated alkynes were obtained (up to 86%). The conditions were quite mild and simply required stirring at room temperature in acetonitrile. Similar to other reports, analogous reactions using NCS were unsuccessful [241]. While only three examples were listed, the high yields and mild conditions were attractive. 

Both chlorines of 1,1-dichloroethylene (340) react stepwise with different terminal alkynes to form the unsymmetrical enediyne 341 [250]. The coupling of the dichloroimine 342 with tin acetylide followed by hydrolysis affords the dialkynyl ketone 343[2511. The phenylthioimidoyl chloride 344 undergoes stepwise reactions with two different tin acetylides to give the dialkynylimine 345[252],... 

Because vicinal dihalides are prepared by addition of chlorine or bromine to alkenes (Section 6 14) alkenes especially terminal alkenes can serve as starting mate rials for the preparation of alkynes as shown m the following example... 

Alkynes react with chlorine and bromine to yield tetrahaloalkanes Two molecules of the halogen add to the triple bond... 

Halogenation (Section 9 13) Addition of 1 mole of chlorine or bromine to an alkyne yields a trans dihaloalkene Atetrahalide is formed on addition of a second equivalent of the halogen... 

Copper Acetylene and alkynes, ammonium nitrate, azides, bromates, chlorates, iodates, chlorine, ethylene oxide, fluorine, peroxides, hydrogen sulflde, hydrazinium nitrate... 

The iodination reaction can also be conducted with iodine monochloride in the presence of sodium acetate (240) or iodine in the presence of water or methanolic sodium acetate (241). Under these mild conditions functionalized alkenes can be transformed into the corresponding iodides. AppHcation of B-alkyl-9-BBN derivatives in the chlorination and dark bromination reactions allows better utilization of alkyl groups (235,242). An indirect stereoselective procedure for the conversion of alkynes into (H)-1-ha1o-1-alkenes is based on the mercuration reaction of boronic acids followed by in situ bromination or iodination of the intermediate mercuric salts (243). 

Chlorination of sodium cyanodithioformate gives 3,4-dichloro-5-cyanoisothiazole (227), probably via the isothiazolodithiine (226) (72AHC(l4)l). The thienoisothiazole (228) undergoes cycloaddition with alkynic esters to give adducts such as compound (229), which... 

Bromine and chlorine also add to alkynes to give addition products, and trans stereochemistry again results. 

Chirality center, 292 detection of, 292-293 Eischer projections and, 975-978 R,S configuration of, 297-300 Chitin, structure of, 1002 Chloral hydrate, structure of, 707 Chloramphenicol, structure of, 304 Chlorine, reaction with alkanes, 91-92,335-338 reaction with alkenes, 215-218 reaction with alkynes, 262-263 reaction with aromatic compounds, 550 Chloro group, directing effect of, 567-568... 

Liquid crystals based on aliphatic isocyanides and aromatic alkynyls (compounds 16) show enantiotropic nematic phases between 110 and 160 °C. Important reductions in the transition temperatures, mainly in clearing points (<100 °C), areobtained when a branched octyl isocyanide is used. The nematic phase stability is also reduced and the complexes are thermally more stable than derivatives of aliphatic alkynes. Other structural variations such as the introduction of a lateral chlorine atom on one ring of the phenyl benzoate moiety or the use of a branched terminal alkyl chain produce a decrease of the transition temperatures enhancing the formation of enantiotropic nematic phases without decomposition. 

Alkynes show the same kind of reactions toward chlorine and bromine that alkenes do They react by addition. 

Most additions of chlorine and bromine to alkynes are anti additions and yield lrans-d haloalkenes. 

The isomerization of the smallest alkynes 80 with halogens in a propargylic position has been described for chlorine [151, 152], bromine [153] and iodine [154] (Scheme 1.35), but often might proceed by an SN2 -type substitution rather than a prototropic rearrangement [155-159]. On the other hand, transformations such as 82 —> 83 [160] or 84 —> 85 [161] are clearly prototropic (Scheme 1.36). This is also true for propargylic halides such as 86 with its additional ester group assisting the prototropic isomerization [162,163] (Scheme 1.37). 

These trends were further confirmed through reactions of the foregoing chiral carbonate and phosphate derivatives with other electrophiles (Eqs. 9.32-9.34) [39]. For example, on protonolysis or deuterolysis, the allenyltitanium intermediate derived from the tertiary carbonate of Eq. 9.32 afforded an alkyne of 90% enantiopurity. Based on the configuration of this product and the assumption of a syn elimination to form the allenyltitanium, the protonolysis was suggested to take place by a syn SE2 pathway. In contrast, chlorination of this allenyltitanium intermediate follows an anti pathway (Eq. 9.33). 

Allenylcobaloximes, e.g. 26, react with bromotrichloromethane, carbon tetrachloride, trichloroacetonitrile, methyl trichloroacetate and bromoform to afford functionalized terminal alkynes in synthetically useful yields (Scheme 11.10). The nature of the products formed in this transformation points to a y-specific attack of polyhaloethyl radicals to the allenyl group, with either a concerted or a stepwise formation of coba-loxime(II) 27 and the substituted alkyne [62, 63]. Cobalt(II) radical 27 abstracts a bromine atom (from BrCCl3) or a chlorine atom (e.g. from C13CCN), which leads to a regeneration of the chain-carrying radical. It is worth mentioning that the reverse reaction, i.e. the addition of alkyl radicals to stannylmethyl-substituted alkynes, has been applied in the synthesis of, e.g., allenyl-substituted thymidine derivatives [64],... 

The acetylene coordinates trans to the least o electron donor group, chlorine. Coordination of the C-H bond is a less favorable alternative to coordination of the n system. The o C-H complex is 17.1 kcal.mol 1 less stable than the rc-alkyne complex (Figure 5). From this c C-H intermediate the 1,2 shift is possible with a relatively small activation barrier (+15.5 kcaLmol 1) to yield the vinylidene complex. However this mechanism is in contradiction with the labeling experiment. 

Alkanes n-butene, isopentane, isooctane Cydoalkanes t dohezane, methylcyclopentane Olefins (sometimes called alkenes ) ethylene, propylene, butene Cydoolefins ( clohezene Alkynes acetylene Aromatics toluene, i ene CHLORINATED HYDROCARBONS ALDEHYDES, RCHO formaldehyde, acetaldehyde KETONES, RCX R " acetone, methylethylketone NITRIC OXIDE, NO ... 

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