Halides acetylenic

The rate of the reaction decreases with increasing number of substituents in the acetylenic halide, and it is higher with acetylenic bromides than with the corresponding chlorides. Methyl magnesium iodide gives equal amounts of 1,1- and 1,3--substitution products, whereas tert.-butylmagnesium bromide does not react. However, for some tert.-butyl substituted allenes there exists an attractive com-... 

Tertiary acetylenic halides give unsatisfactory results owing to further isomerization of the allenic halide into a conjugated diene system under the influence of the copper salt. Bromo- and iodoallenes with the structures R R2C=C=CH-X can also be synthesized by an aqueous procedure, consisting of reaction between... 

Acetylenic Grignard reagents of the type RC CMgBr are prepared not from an acetylenic halide but by an acid-base reaction in which a Grignard reagent abstracts a proton from a terminal aUcyne... 

This reaction illustrates a stereoselective preparation of (Z)-vinylic cuprates, which are very useful synthetic intermediates. They react with a variety of electrophiles such as carbon dioxide, epoxides, aldehydes, allylic halides, alkyl halides, and acetylenic halides they undergo... 

The copper species formed depends on the solvent, and three different species were detected by F NMR, although the structure of each species was not elucidated [245 This copper reagent undergoes a variety of coupling reactions with aryl, alkenyl, allyl, and acetylenic halides [244, 245 (equation 162)... 

With acyl halides, the corresponding acyl phosphonates are obtained. Furthermore allylic and acetylenic halides, as well as a-halogenated carboxylic esters and dihalides, can be used as starting materials. If substituents R and R are different, a mixture of products may be obtained, because the reaction product RX 5 can further react with phosphite 1 that is still present ... 

A closely related reaction of (—)-(S)-276 with the Grignard reagents obtained from a-acetylenic halides leads to the formation of mixtures of acetylenic sulphoxides 290 and allenic sulphoxides 291363 (equation 161). The latter compounds are most probably formed via transition state 292, which is analogous to 289. On the other hand, hex-l-ynyl p-tolyl sulphoxide 293 is smoothly prepared from hex-1 -ynylmagnesium bromide and (— )-(S)-276363 (equation 162). 

This may be regarded as a variation of 10-110 but it must have a different mechanism since acetylenic halides give the reaction but ordinary alkyl halides do... 

Reaction of a sodium salt of a dialkyl phosphite with an acetylenic halide... 

Simple reaction occurs with aryl halides only when the ring is sufficiently substituted with electron-withdrawing functions to allow attack by the nucleophilic phosphorus.53-56 Generally, reaction with aryl halides requires the presence of a Lewis acid catalyst or some other means of reaction initiation. These reactions will be considered in detail in Chapter 6 of this work. Interestingly, while reactions involving vinylic halides seem to correlate with those of aromatic halides (see Chapter 6), acetylenic halides undergo facile reaction with these phosphorus reagents.57 58... 

Several publications deal with acetylenic halides that can undergo reductive intramolecular cyclization [37]. For example, electrolysis of 6-iodo-l-phenyl-l-hexyne at a carbon cathode gives benzylidenecy-clopentane in 36% yield. 

The mechanism of this remarkable reaction, in which a halogen atom in a tertiary acetylenic halide is substituted by the nucleophilic group NH2 with high yields, is not completely dear. Probably the ethynyl hydrogen atom is abstracted in the first step by the strongly basic amide. The results from solvolysis experiments carried out with tertiary acetylenic bromides [22] suggest that the intermediate -C C-C(CH3)2C1 looses CP to give the Zwitter-ionic intermediate C=C-C+(CH3)2. This is subsequently attacked by NH3 or-NH2. 

Carbonylations of olefins, acetylenes, halides, alcohols, amines, nitro compounds, etc., promoted by transition metal complexes are very important in both industrial and laboratory organic syntheses. The mechanisms of those reactions have been studied extensively, especially for those associated with commercial processes. " The research... 

This may be regarded as a variation of 0-100 but it must have a different mechanism since acetylenic halides give the reaction but ordinary alkyl halides do not, which is hardly compatible with a nucleophilic mechanism. However, the mechanism is not fully understood. Propargyl halides also give the reaction.290 A variation of the Cadiot-Chodkiewicz method... 

CH3 CH2 CH=CHC1]. In those cases where the halogen is attached to an sp-hybridised carbon atom in an alkyne, the compounds are called alkynyl (or acetylenic) halides [R C C X, e.g. 1-bromobut-l-yne (3) CH3 CH2 C=CBr], Allylic halides (R CH=CH CH2X) have an sp2-hybridised carbon atom attached to a saturated halogen-carrying carbon [e.g. (E)- l-iodobut-2-ene (4) CH3-CH=CH-CH2I]. 

In the presence of anhydrous Cr(II) halide salts, organic halides undergo one-electron reduction to form radical species, which in the presence of a second equivalent of Cr(II) undergo a second one-electron reduction to form organochromium(III) species (Scheme 5)331. This process works well for allyl, vinyl and acetylenic halides, but not for simple alkyl cases. Alkylchromium(III) species can be formed readily, however, in the presence of catalytic amounts of vitamin B12 or cobalt phthalocyanine (CoPc)332. 

This reaction illustrates a stereoselective preparation of (Z)-vinylic cuprates, 5 which are very useful synthetic Intermediates. They react with a variety of electrophiles such as carbon dioxide,5,6 epoxides,5,6 aldehydes,6 allylic halides,7 alkyl halides,7 and acetylenic halides 7 they undergo conjugate addition to a,6-unsaturated esters,5 6 ketones,6 aldehydes,6 and sulfones.8 Finally they add smoothly to activated triple bonds6 such as HCSC-OEt, HC3C-SEt, HC=C-CH(0Et)2. In most cases these cuprates transfer both alkenyl groups. The uses and applications of the carbocupration reaction have been reviewed recently.9 The configurational purity in the final product 1s at least 99.951 Z in the above transformations. 

The electroreductive cyclization of some acetylenic halides in DMF has been reported by Moore and Peters. 6-Bromo-l-phenyl-l-hexyne (3) gave three polarographic waves at —2-35 V, —2-60 V and — 2-80 V (vs. S.C.E.). The first wave was correlated with C-Br fission ( -hexyl bromide was reduced at —2-29 V) while the two remaining waves corresponded to triple bond reduction (1-phenyl-1-hexyne gave waves at —2-65 V and —2-88 V). The electrolysis reaction mixture contained both five- and six-membered carbocycles as well as straight-chain reduction products... 

---