Coupling of unsaturated halides

Coupling of unsaturated halides with organometallic reagents... 

Reduction of unsaturated halides 0-78 Reduction of allylic alcohols 0-82 Reductive cleavage of enamines 0-86 Coupling of vinylic halides 0-87 Coupling of unsaturated halides with organometallic reagents 0-88 Coupling of allylic halides, tosylates, or acetates... 

Organozinc, organomagnesium or other organometallic species can be effective partners in palladium-catalysed coupling reactions. Metals other than palladium(O), such as nickel(0) or copper(I) (see Section 1.2.1), can alternatively be used to promote cross-coupling of unsaturated halides and organometallic species. ... 

Stille reaction. The preferred catalyst for this coupling of unsaturated halides or triflates with organostannanes has been Pd[P(C6H5)j]4. Much more effective catalysts can be obtained by treatment of Pd2dbu3 with 4 equiv. of various ligands to form a PdL.4 catalyst. Of a number of ligands, the most effective are tri-2-furylphosphine (TFP) and triphenylarsine [As(C6H5)3]. 

The Stille reaction is the palladium-catalyzed coupling of unsaturated halides or triflates with organostaimanes [34]. The accepted mechanism for this reaction is based on the three steps which typically work for this type of cross[Pg.251]

Coupling reactions and related fluoroalkylations with polytTuoioalkyl halides are induced by vanous reagents, among them metals such as copper and zinc, or by an electrochemical cell. More recently, examples of carbon-carbon bond forma tion by coupling of unsaturated fluorides have been reported Both acyclic and cyclic fluoroolefins of the type (Rp)2C=CFRp undergo reducUve dimerization on treatment with phosphines [42] (equation 33) The reaction shown in equation 33 IS also accompbshed electrocheimcally but less cleanly [43]... 

Muller and co-workers reported the three-component one-pot synthesis of various pyrimidines through the in situ generation of unsaturated carbonyl compounds. The palladium catalyzed coupling of aryl halides bearing electron withdrawing substituents 7 with propargyl alcohols 8 produced unsaturated carbonyl compounds 9 after isomerization, which condensed with amidines 10 to form triaryl pyrimidines 11 . 

The combination of the formation of palladium(II) complexes in the oxidative addition of unsaturated halides onto palladium(O), and the palladium(II) mediated ring closure of olefins allows for the elimination of the oxidant. The ring closure of the methallyl-aniline derivative shown in 3.67. in the presence of /J-bromostyrcnc and a catalytic amount of palladium led to the ring closed - coupled product.84 The ring closure might also be accompanied by other follow-up reactions. 2-Methallyl-anilines were converted for example to indolylacetic acid derivatives in the presence of carbon monoxide.85... 

In a thorough study it was determined that the Barbier coupling of allylic halides 69a to aldehydes, ketones, or a,p-unsaturated carbonyl compounds 68 catalyzed by Cp2TiCl2 47a in the presence of manganese as the terminal reducing agent proceeds most likely via a radical mechanism (Fig. 21) [149,150], The active titanocene(III)... 

The palladium-catalyzed coupling of homoallylzinc halides can also be used with jS-bromo-a./J-unsaturated carbonyl derivatives (equation III).11... 

Ullmann reaction Semmelhack (4, 33) has shown that bis( 1,5-cyclo-octadiene)nickel(O) and tetrakis(triphenylphospine)nickel(0) are useful reagents for coupling of aryl halides (Ullmann reaction). However, these zerovalent nickel complexes are not easy to prepare and are extremely sensitive to moisture. Kende reasoned that the coordinatively unsaturated Ni(TPP)3 is actually the species involved and indeed found that aryl halides couple to biaryls in the presence of 1 eq. of this complex. Aryl halides with two orr/io-substituents do not couple. Otherwise, yields of biaryls are in the range of 60-80%. 

Larock, R.C., Leung, W.Y. and Stolz-Dunn, S. (1989) Synthesis of aryl-substituted aldehydes and ketones via palladium-catalyzed coupling of aryl halides and non-allyUc unsaturated alcohols. Tetrahedron Lett., 30, 6629-32. 

Formation of Dienes and Enynes by Coupling and Cross Coupling. The vinylation of methyl acrylate, methyl vinyl ketone, or acrolein with ( ) or (Z) vinylic halides under phase-transfer conditions gives high yields of (E,E) (eq 19) or E,Z) (eq 20) conjugated dienoates, dienones, and dienals, respectively. Coupling of vinyl halides or triflates with a,p or 8, /-unsaturated acids under phase-transfer conditions yields vinyl lactones. ... 

In another method for the coupling of two different allylic groups, a carbanion derived from a P,y-unsaturated thioether couples with an allylic halide. The... 

Nickel-bpy and nickel-pyridine catalytic systems have been applied to numerous electroreductive reactions,202 such as synthesis of ketones by heterocoupling of acyl and benzyl halides,210,213 addition of aryl bromides to activated alkenes,212,214 synthesis of conjugated dienes, unsaturated esters, ketones, and nitriles by homo- and cross-coupling involving alkenyl halides,215 reductive polymerization of aromatic and heteroaromatic dibromides,216-221 or cleavage of the C-0 bond in allyl ethers.222... 

An intermediate acylnickel halide is first formed by oxidative addition of acyl halides to zero-valent nickel. This intermediate can attack unsaturated ligands with subsequent proton attack from water. It can give rise to benzyl- or benzoin-type coupling products, partially decarbonylate to give ketones, or react with organic halides to give ketones as well. Protonation of certain complexes can give aldehydes. Nickel chloride also acts as catalyst for Friedel-Crafts-type reactions. 

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