Coupling with benzyl halides

In a similar way to allyl chloride, benzyl halides also react smoothly with zirconacyclopentadienes in the presence of CuCl. An interesting reaction is shown in Eq. 2.35, whereby the benzo-type eight-membered ring compound 49 can be prepared [7j]. 

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The coupling with benzyl halides is carried out under conditions similar to those used for aUyl chlorides [162]. The selective coupling is achieved by an electron-rich... 

The coupling with benzyl halides was carried out under similar conditions used for allyl chlorides (Equation (59)).314... 

The palladium-catalyzed enyne synthesis is achievable via the decarboxylative coupling of propiolic acids with alkenyl bromides (Scheme 4.62) [63]. Propiolic acids also couple with benzyl halides through decarboxylation and subsequent sp C-sp C bond formation (Scheme 4.63) [64]. 

The homo-coupling of benzylic halides appears to proceed via benzylnickel intermediates similar to that of aryl halides. The intermediate, benzylnickel halide, was successfully trapped with electron deficient olefins. 

Fu s group showed more recently that ot-bromo ketones 6b can be coupled with arylzinc halides catalyzed by 5 mol% NiCl2 DME and 6.5 mol% of PyBOX ligand 5e with good asymmetric induction providing benzylic ketones in 71-93% yield and 72-96% ee (entry 12) [54]. The lower ee values were obtained with orf/io-substituted aryl bromo ketones, while orf/to-substituted arylzinc reagents as well as a-branched bromo ketones did not react. 

The coupling occurred at the less-hindered terminal carbon giving thermally stable ( )-allyl boronates. Thus, the (.E)- and (Z)-crotyl chloride, and 3-chloro-l-butene, all afforded an (A)-crotyl boronate. The reaction with benzyl halides gave benzyl boronates.333... 

The alkenylindium compounds, obtained by the addition of benzyl- and allylindium to alkynes, couple with organic halides in the presence of a palladium catalyst to give the three-component coupling products (Scheme 99).286 1,3-Dibromopropene or 3-bromo-l-iodopropene reacts with indium to give diindiopropene 87a,b.147,148 This dimetallic reagent reacts with two different electrophiles successively carbonyl compounds and imines are allowed to react with 87 as the first electrophile to give vinylic indium intermediates 88, which react with... 

Benzyl ketones. Ni(0) is a useful catalyst for coupling of benzyl halides with acyl halides to form benzyl ketones, AK-HjCOR, in 40-85% yield.-... 

Methylenation. The reagent reacts with ketones at - 10° to give essentially quantitative yields of the corresponding methylene derivatives. The reagent effects coupling of benzyl halides to bibenzyl (85% yield). 

The coupling of benzyl halides with stannanes has been occasionally used in synthesis.One illustrative example is the total syntheses of piericidin A1 (119) and B1 (120).i2o in these syntheses a heterobenzylic Stille cross-coupling reaction of 116 with alkenylstannane 117 proceeded in the presence of a Pd(0) complex bearing bulky PrBuj as the ligand to give key intermediate 118 (Scheme 5.4.23). 

The BiBrs-Sm binary reagent promotes reductive C-S and C-Se bond formation between benzyl and allyl bromides and diorganyl disulfides and diselenides in aqueous media, affording the corresponding sulfides and selenides, respectively (Scheme 14.105) [217, 218]. Intramolecular reductive C-S bond formation by use of a BiCl3-M (M = Sn, Zn) redox system is used in the synthesis of 3-hydroxyceph-ems and 2-exo-methylenepenams (Scheme 14.106) [219]. Alkyl and arylsulfonyl chlorides couple with allylic halides in the presence of Bi to afford the corresponding allylic sulfones [220]. 

In related Pd(Xantphos)-catalyzed cross-couplings of benzyl halides, reductive elimination was proposed as the slow step, since the overall rate increased with large bite angle ligands [98], P-C bond formation with isolated diastereomers of dinucleoside H-phosphonates was stereospecific, likely with retention of configuration at phosphorus, as above (Scheme 58). 

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