Halides alkynyl

Aryl, Alkenyl, Benzyl, and Alkynyl Halides, and Their Pseudo-Halides... 

Some recent studies have underlined the effect that certain physical properties of the reaction medium have in governing the nature and yields of the products obtained when indole Grignard reagents react with alkyl or alkynyl halides. Such factors include the basicity and dielectric constant of the medium and its ability to solvate any of the reacting species. ... 

Palladium-catalyzed carbon-carbon bond forming reactions like the Suzuki reac-tion as well as the Heck reaction and the Stille reaction, have in recent years gained increased importance in synthetic organic chemistry. In case of the Suzuki reaction, an organoboron compound—usually a boronic acid—is reacted with an aryl (or alkenyl, or alkynyl) halide in the presence of a palladium catalyst. 

Alkynes (see also Alkynyl Halides, Alkynyl Ethers)... 

This reaction works with aryl, allylic and 1-alkynyl halides, but not vinylic halides. A vinylic group can be introduced into the 4 position of an isoquinoline by using PdBr2 as the electrophile and an alkene (Scheme 9).10 This process... 

The second reason for the lower yields is the high reactivity of the intermediate. Two molecules of the alkynyl bromide react in a stepwise manner with the zirconacyclopentadiene. When one alkynyl halide molecule couples with the zirconacyclopentadiene, the intermediate bears a metalladienyne moiety (as in 50), as shown in Eq. 2.36... 

The remaining alkenyl copper moiety in 50 can react intramolecularly with the carbon—carbon triple bond to give metallofulvene derivatives 53. However, the coupling of the intermediate with the second molecule of alkynyl halide would seem to be faster than the cyclization reaction. Therefore, the dienediyne is obtained as the major product. 

An entirely different situation is found in alkynyl halides. Here only examples in which the rearrangement is supported by carbonyl groups [106, 164] or electron-withdrawing pentafluorophenyl groups [165] are known. As one example, the selective reaction of the alkynyl bromide next to the carbonyl group, in the presence of a second alkynyl bromide with a propargylic C-O sigma bond, is shown (88 —> 89) [164] (Scheme 1.38). 

A large variety of cuprates are known nowadays. They include heteroleptic derivatives R(Y)CuM (Y = alkynyl, halide, amido, alkoxide, thiolato, phosphide M = Li or Mg), and have found widespread application in organic chemistry. Their syntheses and applications are discussed in the other chapters of this book. In addition, compounds in which the copper to lithium (or magnesium) ratio differs from 1 1 are also known examples are R3CuLi2 and the so-called higher order cyanocuprates introduced by Lipshutz et al. [99]. 

Recently, this methodology has been extended to the couphng of alkyl, allyhc, 1-alkenyl and 1-alkynyl halides with 1-alkenyl and even alkyl boron reagents. 

Bis-acetylene synthesis from alkynyl halides and alkynyl copper reagents. Cf. Castro-Stephens reaction. 

While the mechanisms of these reactions have not been investigated in detail, it is likely that an intermediate copper(I) alkynyl is formed, which undergoes an alkynyl-halide exchange with the metal halide, resulting in the formation of the transition metal cr-alkynyl complex and a Cu(I) halide, which completes the catalytic cycle (Scheme l), ... 

Alkynyl halides are possible monomers for the cross-coupling polymerization, in which boronic acids are used as the organometallic counterparts. For example, bifunctional boronic acid 46 is allowed to react with l,4-di(bromoethy-nyl)benzene 138 to afford the corresponding PAE 139 as shown in Equation (64). Polymerization proceeds at room temperature in toluene in the presence of silver(i) oxide as an activator of the boron reagent. The polymer 139 is obtained in 30-50% yield showing color of red-brown to deep red-brown and slight solubility in toluene (<0.1 wt.%). The molecular weight (Mr of 139 was 1700-4300 (PDI = 1.3-3.6). 

Alkynylchromium compounds.1 Alkynyl halides react with CrCl2 (or CrCl3/ LiAlH4) to form unisolable alkynylchromium compounds, which undergo selective 1,2-addition to aldehydes. 

General methods of preparation for alkenyl and alkynyl halides are listed in Table 14-5. By the alkynyl halides we mean 1-halo-alkynes. One interesting method by which they may be prepared employs 1-alkynes with hypohalites ... 

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