Cross-coupling reaction with allylic halides

Cross-coupling reactions with allylic halides are especially high-yield reactions. They occur with high S 2 selectivity, in contrast to the corresponding Pd " - or Ni -catalyzed reactions which give the S ,j2 product (Scheme 9-18) [44-46]. 

Cross-coupling Reactions with Allylic Halides and Related Reactive Halides... 

Allylic barium reagents prepared in this way can realize highly a-selective reactions with different electrophiles, e.g. cross-coupling reactions with allylic halides or allylic phosphates, additions to carbonyl compounds or imines, and ring opening of epoxides. A selective Michael addition reaction with an a,/ -unsaturated cy-cloalkanone can also be performed by use of an allylic barium reagent. 

E. Cross-coupling Reactions with Allyl and Propargyl Halides..1283... 

Allylindium reagents can be utilized in the Pd-catalyzed cross-coupling reaction with aryl halides. The Pd-catalyzed allylic substitution of allyl carbonate produces 1,5-dienes (Scheme 103).353-355... 

Allyltrifluorosilanes undergo the cross-coupling reaction with aryl halides exclusively at the y-carbon to give allylated products (Eq. 27) [32]. The /-selectivity is noteworthy, because the cross-coupling reaction using other allylmetals usually takes place via a-attack. 

Although the cross-coupling reaction with organic halides generally requires the assistance of bases, allylic phenoxide and cinnamyl acetate react with 1-alkenylborates under neutral conditions to yield 75% and 12%, respectively, of the corresponding 1,4-dienes (Scheme 2-21) [45, 54]. Thus, the jT -(allylphenoxo)- and r-... 

Allylic zinc reagents undergo cross-coupling reactions with reactive halides leading to 1,5-dienes. Usually the new carbon-carbon bond is formed from the more-substituted end of the allylic system (Scheme 9-11) [30]. 

The 1,4-conjugate addition of triorganoindium to enones is promoted by a catalytic amount of Ni(COD)2 (Scheme 8.71) [100], Allylindium reagents can be used in Pd-catalyzed cross-coupling reaction with aryl halides (Scheme 8.72). The Pd-catalyzed allylic substitution of allyl carbonate produces 1,5-dienes (Scheme 8.73) [101]. The indium-mediated palladium-catalyzed Ullmann-type reductive coupling of aryl halides proceeds in aqueous media under air (Scheme 8.74) [102]. 

Organozinc halides undergo a Pd-catalyzed carbonylative cross-coupling reaction with allylic benzoates and phosphates to furnish allyl alkyl ketones under 1 atm of CO (Scheme 24).In Table 2 are summarized typical examples for the reaction with /3-... 

The scope of transition metal-catalysed cross-coupling reactions involving N-tosylhydrazones has been broadened. While IV-tosylhydrazones cross-couple with trialkylsilylethynes to form C -C s bonds under Cu(I) catalysis,i° Pd(0) catalysis has been used to induce (i) their oxidative cross-coupling reactions with allylic alcoholsi and (ii) their cross-coupling with cyclopropyl halides, giving rise to... 

Oxidative addition of the carbon-halogen bond is a well-documented reaction for Group 10 transition metal complexes, but it is relatively limited for ruthenium. The example given here involves the reversible oxidative addition of allyl halide to RuCp(CO)2X to produce RuCp(p -allyl)X2 [78]. Oxidative addition of allyl halide to a Ru(0) complex Ru(l,5-COD)(l,3,5-COT) is also reported, but the product yield was poor [79]. Nevertheless, a catalytic Heck-type alkenylation of bromostyrene with methyl acrylate by Ru(l,5-COD)(l,3,5-COT) proceeded smoothly [80]. A cross-coupling reaction of alkenyl halide with Grignard reagents or alkyl lithium also pro-... 

The cross-coupling reaction of organoboron compounds with organic halides or triflates proceeds selectively in the presence of a base, such as sodium or potassium carbonate, phosphate, hydroxide, and alkoxide [11, 45], The bases can be used in aqueous solution, or in suspension in dioxane or DMF. In contrast, the cross-coupling reaction with certain electrophiles, such as allylic acetates [45], 1,3-butadiene monoxide [49], and propargyl carbonates [50], occurs under neutral conditions without any assistance from a base. The transmetallation of organoboron compounds with palladium halides under basic or neutral conditions can be considered to involve three routes, 1, 2, and 3 (Schemes 2-18, 2-20, and 2-23, below). 

Oxidative addition [1, 38] of 1-alkenyl, i-alkynyl, allyl, benzyl, and aiyl halides to a palladium(O) complex affords a stable rra .s-<7-palladium(II) complex (11). The reaction proceeds with complete retention of configuration for alkenyl halides and with inversion for allylic and benzylic halides. Alkyl halides having /3-hydrogens are rarely useful because the oxidative addition step is very slow and may compete with /3-hydride elimination from the a-organopalladium(II) species. However, it has been recently shown that iodoalkanes undergo the cross-coupling reaction with organoboron compounds (Section 2.4.5). 

Stille cross-coupling reactions of allylic and benzylic halides with conjugated organo-... 

Homo- and cross-coupling reactions of allyhc halides and reactions of conjugated dienes with dichloroalkanes using reactive barium are reviewed in Section 5.2. The next section covers methods of generating allylic barium reagents and reactions of these carbanions with a variety of electrophiles. The last section describes examples of other carbon-carbon bond forming reactions promoted by barium compounds. 

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