Allyl bromide coupling reaction with

As well as alkenylstannanes [106-108], other classes such as a-heteroatom-substituted alkyltributylstannanes [109] and, more importantly, allylic stannanes [110, 111] also undergo these Sn-Cu transmetalations. Otherwise difficult to prepare, allylic copper reagents may, however, be obtained by treatment of allylic stannanes (produced in turn from organolithium, magnesium, or zinc organometallics) with Me2CuLi LiCN. They enter into cross-coupling reactions with alkyl bromides [110] or vinyl triflates (Scheme 2.52) [111]. 

When the metallic additive to the intermediate 374 was zinc dihalide (or another Lewis acid, such as aluminum trichloride, iron trichloride or boron trifluoride), a conjugate addition to electrophilic olefins affords 381 . In the case of the lithium-zinc transmetallation, a palladium-catalyzed Negishi cross-coupling reaction with aryl bromides or iodides allowed the preparation of arylated componnds 384 ° in 26-77% yield. In addition, a Sn2 allylation of the mentioned zinc intermediates with reagents of type R CH=CHCH(R )X (X = chlorine, bromine) gave the corresponding compounds 385 in 52-68% yield. ... 

Mowery and DeShong used the commercially available hypervalent silicate complex TBAT as a phenylating agent for the cross-coupling reaction with allylic esters. They later reported on the use of the same organosilane for the coupling with aryl iodides and triflates and electron-deficient aryl bromides. The reactions were catalyzed by either Pd(dba)2 or [Pd(allyl)Cl]2 without the need of added phosphine ligands. 

Directed coupling reactions, where no cross-coupling may occur, requires the reagents derived from the appropriate synthons to be ionically different at the reactive site. The carbon-carbon coupling reaction to form hept-l-ene (Expt 5.8), illustrates the importance of selecting the reactive, and readily available, allyl bromide (cationic site) with butylmagnesium bromide (anionic site) (A), rather than the other alternative (B). 

The more reactive ft -carbon atom of ketone a,/ -dianions can be regiospecifically coupled with alkyl halides to give first lithium enolates, which are then trapped by more reactive carbon electrophiles such as allylic halides. The first example shown in Table 8 deals with the sequential /1-alkylation and ce-allylation of a ketone a,/1-dianion1 13. Thus, the dianion underwent regioselective alkylation at the ft carbon with //-pentyl bromide and then allylation with allyl bromide at the a carbon. When an excess of allyl bromide is reacted with the a, ft -dianion, the diallylated product is obtained in a good yield, whereas a threefold excess of pentyl bromide only resulted in the formation of the ft-alkylation product. Similar consecutive alkyl/allyl-type reactions are also possible for ketone a,5-dianions14. 

Hydrolysis of the reaction mixture afforded 63 in 80% yield as a single cis diastereomer, and the formation of cyclic organozinc bromide was checked by iodinolysis, by coupling reactions with vinyl iodides in the presence of a catalytic amount of Pd(PPh3)4, or by reaction with allyl halides after transmetallation of the organozinc bromide into an organocopper reagent [60] (Scheme 7-53). 

It was shown that alkyl bromides react without a catalyst with allylmagnesium bromide in THF. However, because allyl bromide reacts quantitatively with magnesium in THF to give 1,5-hexadiene by a Wurtz-coupling reaction, allylmagnesium bromide can be obtained in this solvent only by solvent exchange ... 

Recently, Shibata and co-workers found that aryl(trimethoxy)silanes were also applicable to the Pd-catalyzed cross-coupling reaction with aryl bromides (Scheme 14). A similar procedure using phenyl-, vinyl- and allyl(trialkoxy)silanes was also reported by Mowery and DeShong. ... 

In addition to the above-mentioned allylic alkylation reactions, catalytic-in-copper C(sp )-C(sp ) cross-coupling reactions with alkylzincs can be achieved with some other specific electrophiles. For instance, the benzylzinc reagent 127, prepared in the presence of LiCl, undergoes coupling with the benzyl bromide 128 in the presence of only 0.4mol% CuCN-2 LiCl, with a yield of 89% (Scheme 4.29) [112, 113]. 

In 1993, Corriu et al. studied the synthesis of nitrogen-containing heterocycles from (Z)-3-(tribulylstannyl)allylamine, which was prepared by the reaction of Af-(trimethylsilyl)allylamine with 2 mol of ra-butyllithium followed by treatment with chlorotributyltin and subsequent hydrolysis. The unprotected (Z)-3-(tributylstannyl)allylamine underwent a palladium-catalyzed cross-coupling reaction with aromatic bromides affording a stereospecific preparation of substituted allylic amines with Z configuration of the carbon-carbon double bond. The reactions of o/t/zo-functionalized aryl bromides offer a one-step preparation of 7-membered nitrogen heterocycles in high yields (Scheme 4.18). 

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