Zinc alkyls iodide

Alkyl zinc iodides RFG—Zn—I are poor nucleophiles. However, they are turned into good nucleophiles when they are converted into the so-called Knochel cuprates RFG— Cu(CN)ZnHal with solubilized CuCN—that is, CuCN containing LiHal. In the presence of a Lewis acid Knochel cuprates add to aldehydes, provided these are a,/f-unsaturated. With substituted oc,/3-unsaturated aldehydes a 1,2-addition can be observed, as shown in Figure 10.38. With acrolein (an unsubstituted f/./l-u nsaturated aldehyde) or a,/J-unsaturated ketones (Fig. 10.43), however, Knochel cuprates undergo 1,4-additions. 

Alkyl zinc iodides RFG—Zn—I are poor nucleophiles. However, they are turned into good nucleophiles when they are converted into the so-called Knochel cuprates Rfg—Cu(CN)ZnHal with solubilized CuCN—that is, CuCN containing LiHal. Knochel cuprates add to aldehydes in the presence of Lewis acid, as shown in Figure 8.29. 

Other coupling partners to organozinc reagents include heterocyles such as 2-methylthiobenzothiazole, alkenyl aryl iodonium triflates (alkenyl group transfer for synthesis of trisubstituted alkenes), and aryl heteroaryl ethers. " Improved nickel-catalyzed cross-coupling conditions between oz-rto-substituted aryl iodides-nonaflates and alkyl-zinc iodides in. solution and in the solid phase have been defined. ... 

Scheme 7.34 Stereoselective preparation of secondary alkyl-zinc iodides by the direct insertion of zinc.

Aziridines have been synthesized, albeit in low yield, by copper-catalyzed decomposition of ethyl diazoacetate in the presence of an inline 260). It seems that such a carbenoid cyclopropanation reaction has not been realized with other diazo compounds. The recently described preparation of 1,2,3-trisubstituted aziridines by reaction of phenyldiazomethane with N-alkyl aldimines or ketimines in the presence of zinc iodide 261 > most certainly does not proceed through carbenoid intermediates rather, the metal salt serves to activate the imine to nucleophilic attack from the diazo carbon. Replacement of Znl2 by one of the traditional copper catalysts resulted in formation of imidazoline derivatives via an intermediate azomethine ylide261). 

Under the above-described conditions, esters are nnaffected and aliphatic ketones are barely rednced. In the presence of zinc iodide, however, aliphatic ketones, as well as aldehydes and aromatic ketones, are converted into methyl ethers in high yields. If alcohols other than methanol are nsed, the corresponding alkyl ethers are obtained. 

Although O-alkyl-substituted enol ethers react smoothly with zinc carbenoids (eqna-tion 18) , higher yields are usually obtained with the Fnrnkawa reagent nsing a slight excess of diethylzinc to scavenge zinc iodide (and convert it into the less Lewis acidic ethylzinc iodide as it is formed) (see equation 18 vs 19). ... 

Tributyltin hydride, 316 Zinc iodide, 280 From alkyl halides Lithium aluminum hydride-Ceri-um(III) chloride, 159 Palladium catalysts, 230 Sodium cyanoborohydride-Tin(II) chloride, 280 From alkyl sulfonates Lithium triethylborohydride, 153 From thiols... 

With the development of the cross coupling methodology, many 6-C-substituted purines have been prepared in the past decade. Thus, 6 halopurine derivatives react with arylmagnesium halides,25 alkyl(aryl)zinc or tin reagents,26 trialkylaluminum,27 or alkylcuprates28 to give the 6-alkylpurine derivatives. Also a reverse approach based on the reaction of purine-6-zinc iodide with aryl or vinyl halides has recently been described.29 For the synthesis of 6-arylpurines, an alternative approach makes use of radical photochemical reactions of adenine derivatives with aromatic compounds,30 but this method is very unselective and for substituted benzenes, mixtures of ortho-, meta-, and para substituted derivatives were obtained. 

Allylcopper/zinc reagents can be prepared directly by reaction of vinyl copper reagents with (iodomethyl)zinc iodide, the Simmons-Smith reagent. These allylcopper/zinc reagents do not couple with an alkyl iodide or benzyl bromide, but react readily with electrophiles such as aldehydes, ketones, or imines.3 This approach to organodimetallic reagents is apparently limited (see Iodomethylzinc iodide, this volume). 

Fig (16) The enone (131), prepared from (130) is alkylated with iodide (133) to obtain the product (134). It reacts with trimethylsilyl cyanide and zinc iodide. The resulting product (135) is converted to tricyclic compound (136) by heating with hydrochloric acid and ethanol. 

Unsymmetrical alkyl phenyl tellurium derivatives were prepared in good yields from phenyl trimethylsilyl tellurium and epoxides, carboxylic acid esters, and linear or cyclic ethers under very mild conditions. In these reactions, which proceed in dichloromethane in the presence of a catalytic amount of zinc iodide, a carbon-oxygen single bond is cleaved. The highly nucleophilic benzenetellurolate binds to the carbon fragment, whereas the trimethylsilyl group becomes linked to the oxygen. 

In the case of the allenyl copper intermediate 724, its alkylation with (iodomethyl)zinc iodide and carbonyl compounds afforded dienes 7251032 (Scheme 189). 

Phenylseleneny lotion of acetates and lactones. In the presence of zinc iodide, 1 reacts with alkyl acetates to form alkyl phenyl selenides. The reaction is particularly facile with acetates of tertiary, ailylic, and benzylic aicohols. Acetates of primary and secondary alcohols react only at 110°. 

Edward Frankland (1825-1899) discovered the first transition metal alkyl complexes - diethylzinc ( mobile fluid") and ethyl-zinc iodide ( white mass of crystals ) - while he worked in Robert Bunsen s Marburg laboratory (1849). Frankland was later a professor of chemistry in London. Alkyl-metal bonding occurs in practically all catalytic processes involving hydrocarbons, e. g., hydroformylation (Section 2.1.1), hydrogenation of olefins (Section 2.2), hydrocarbon activation (Section 3.3.6), and C-H-activation (Chapter 4). 

The Negishi coupling started with the synthesis of the zinc iodide reagent (Table 5.2, Scheme 5.19). The zinc was activated by a modification of the Knochel procedure, then reacted with a solution of iodide 42 in DMAC to provide the desired alkyl zinc species. The zinc insertion was run in the presence of 5 weight% of CelPure P65 to aid in the filtration of excess zinc from the insertion reaction mixture. The resulting solution was stable at 22°C under Nj for >6 months. 

Before we leave this section on cyclopropanes, we want you to take a step back from simply thinking about carbenes, and consider the types of reagents that form three-membered rings generally. They all have something in common, which we could call -enoid character. Cyciopropanes form when a carbene (which, in the singlet state, has an empty, electrophilic p orbital and a full, nominally nucleophilic sp orbital) attacks alkenes. The Simmons-Smith carbenoid is not a carbene, but nonetheless has a carbon atom with joint nucleophilic (alkyl zinc) and electrophilic (alkyl iodide) character. When... 

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