Diorganozinc reagents

In mosl allylation reactions, only a catalytic amount of CuCN-2LiCl is required [41]. Use of die chiral ferrocenylamine 104 as a catalyst makes enables asymmetric allylation of diorganozinc reagents to be effected witli allylic chlorides iScbeme 2.3G) [78]. Related electropb des such as propargylic bromides [79] and unsaturated epoxides [80] also undergo Su2 -substitution reactions iScbeme 2.37). 

Figure 84 Imine derivatives alkylated by diorganozinc reagents.

Figure 85 Examples of chiral ligands used for the alkylation and arylation of imines by diorganozinc reagents.

Scheme 11.23. Preparation of various functionally substituted aminocyclopro-panes from diorganozinc reagents 80 and N,N-dialkylcarboxamides [119],...

Phosphorus-Based Ligands in the Catalyzed Addition of Diorganozinc Reagents... 

Knochel and co-worker (187) described an effective catalyst for the SN2 delivery of organozinc reagents to allylic chlorides. Optimal selectivities are observed when bulky diorganozinc reagents such as 257 are used, Eq. 149. The early results in this area are promising, although the requirement for 10-fold excess of ligand 259 makes this reaction rather impractical. 

The related zinc cuprates formed from diorganozinc reagents and copper(I) cyanide also undergo smooth SN2 substitution reactions with propargyl oxiranes in the presence of phosphines or phosphites (Scheme 2.12). These transformations can also be performed with catalytic amounts of the copper salt since no direct reaction between the organozinc reagent and the substrate interferes [31, 34], and therefore should also be applicable to functionalized organozinc compounds. 

Scheme 2.36. Enantioselective allylation with diorganozinc reagents.

To conclude the study, combinations of differently substituted substrates and diorganozinc reagents were investigated (Scheme 8.23). 

Functionalized diorganozinc reagents [AcO(CH2)4]2Zn and [Et02C(CH2)3]2Zn were also employed, giving complete y selectivity in both cases, with ees of 50%. 

Woodward et al. have used the binaphthol-derived ligand 40 in asymmetric conjugate addition reactions of dialkylzinc to enones [46]. Compound 40 has also been studied as a ligand in allylic substitutions with diorganozinc reagents [47]. To allow better control over selectivity in y substitution of the allylic electrophiles studied, Woodward et al. investigated the influence of an additional ester substituent in the jS-position (Scheme 8.25). 

This class of ligands produces ligand-accelerated catalysis of the 1,4-addition of diorganozinc reagents to a variety of substrates, see ref. 37. 

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