Alkylzinc derivatives

Although not widely applicable at this moment, treatment of alkyl iodides with Et2Zn in the presence of a catalytic amount of Cul or CuCN can provide the corresponding alkylzinc derivatives by a radical process8a,b. 

SCHEME 81. Synthesis of amphidinolide T1 via Pd-catalyzed acylation of an alkylzinc derivative... 

Non-aromatic organolithium compounds can be prepared by transmetallation of resin-bound stannanes [25] or by deprotonation of alkynes [26], triphenylmethane [27], or other resin-bound C II acidic compounds with lithium amides or similar bases (Figure 4.3). The reaction of polystyrene-bound trialkylboranes with diethylzinc yields resin-bound alkylzinc derivatives [28]. 

Benzotriazole is an excellent leaving group, and the readily available imidazolidin-2-ones react with aryl-, alkenyl-, or alkylzinc derivates via an elimination-addition mechanism providing the /raor-products with >99% diastereo-selectivity (Equation (65)).125 Propargylic mesylates such as fluorine-substituted derivatives react with PhZnCl in the presence of Pd(PPh3)4 (5mol%) to provide the anti-S Z -product in excellent yield and complete transfer of the stereochemistry leading to the allene species (Equation (66)).126... 

Although alkylzinc derivatives add only slowly to aldehydes, alkenylzinc derivatives display a higher reactivity (Equation (74)).142 Reactive benzylic or related zinc reagents smoothly add to aldehydes, providing the allylic alcohol in almost quantitative yield (Equation (75)).143... 

Multinuclear aggregates of alkylzinc derivatives have been prepared and structurally characterized by the reaction between tris(3,5-dialkyl-2-hydroxyphenyl)methanes with dimethyl- or diethylzinc. Depending on both the steric... 

Remarkably, the methyl group is not transferred in these cross-coupling reactions. Interestingly, the reaction can be extended to secondary alkylzinc derivatives (Scheme 9-29) [58]. 

Bis- and tris(pyrazolyl)borato ligands have been widely used to stabilize a variety of alkylmetal complexes among which several alkylzinc derivatives. Stable monomeric three-coordinate alkylzinc complexes, B (3-... 

Similarly, the high reactivity of organozincs tends to preclude the CO insertion-crosscoupling tandem process, which proceeds well with slower reacting organotins. However, some chelation-stabilized alkylzinc derivatives do satisfactorily participate in this tandem process (Scheme 11). It should also be recalled that the Pd-catalyzed reaction of organozincs with acyl halides without the use of CO is one of the most general routes to ketones. ... 

Scheme 3.60 Pd-catalyzed Negishi coupling between primary alkylzinc derivatives and primary alkyl electrophiles [233].

Scheme 3.61 Pd-catalyzed cross-coupling of primary alkylzinc derivatives with primary alkyl electrophiles in the presence of Pd-NHC catalysts in THF/NMP [235].

Scheme 3.78 Application of Pd-catalyzed acylations of alkylzinc derivatives in the synthesis of amphidinolide T1 [256].

Entry Alkylzinc derivative Method of generation" a-lodoenoe Product yield (%)"... 

Functionalized alkyl iodides undergo an I-Zn exchange in a simple uncatalyzed reaction with an excess of diethyl zinc. The driving force of this reaction is the formation of a volatile component (ethyl iodide) from the reaction mixture. Also, the C-Zn bond in Et2Zn is much more reactive and less strong than the C-Zn bond in higher alkylzinc derivatives. 

Scheme 7.11 Preparation of alkylzinc derivatives starting from alkyl sulfonates.

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