Benzylzinc reagents

AngioleUi, M. E., Casalnuovo, A. L. and Selby, T. P. 2000. PaUadimn-catalyzed cross-coupling of benzylzinc reagents with methylthio A-heterocycles A new coupling reaction with unusual selectivity. Synlett 6 905-907. 

Scheme 3.3 Pd- or Ni-catalyzed aryl-aryl or benzyl-aryl coupling reactions with alkylzinc or benzylzinc reagents [22a].

Both of these reactions produce diaryhnethanes, and the first examples of the Pd-catalyzed benzyl-aryl coupling were reported in 1977 [22aj. In many cases, however, Ni catalysts were similarly effective. Both types of reactions have since been successfully employed in a variety of cases, including those involving heteroaryl groups, as shown in Scheme 3.47. Recent developments toward the direct synthesis of benzylzinc reagents through the use of LiCl as promoter are noteworthy [183]. 

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]. 

During the past decade, the main focus of studies related to the well-known349 CeCl3- or SnCl2-catalyzed reactions of allylzinc and benzylzinc halides with imines was the application of polymer-supported chiral imines.350,351 An example of such reactions is shown in Scheme 135.350 It should be noted that attempts using arylzinc reagents in... 

Unlike the analogous Grignard reagent, benzylzinc(II) chloride reacts with phosgene to give two products, one ring substituted, the other side-chain substituted [1020] ... 

Zn alkyls, generated in situ, are very versatile reagents for alkyl-alkyl, alkyl-aryl and aryl-aryl couplings [73]. Arylzinc bromides and benzylzinc iodides may serve as more reactive substitutes for boronates or stannanes in Pd-mediated couplings. 

C.ii.c. Benzyl Alkenyl Coupling. As in the cases of benzyl-aryl coupling, benzylzincs appear to be the reagents of choice, although comparative data are virtually absent. Some representative results are shown in Table 8. 

Cunico and Pandey reported the palladium-catalyzed preparation of a-aryl tertiary amides using benzylic halides and carbamoylsilane [87], and, in this report, a disadvantage of using aminocarbonylation of benzyl halides was also described [90]. Accordingly, to expand the scope of this chemistry, we next focused on the use of benzylic organometallic reagents to develop a facile route for the synthesis of a-aryl tertiary amides. Since the appropriate benzylzinc halides were easily prepared via the direct insertion of highly active zinc, they were employed in the... 

A novel migration-addition sequence has been found for enantioenriched N-t-butylsulfinyl iminoacetate (31) with functionalized benzylzinc bromide reagents, producing t-leucine derivatives (32) in up to 96% de Desulfurization and A-protection 0 to give (33) can then be carried out in >98% ee. (fA... 

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