Phenylzinc

The carbonylation of aryl iodides in the presence of alkyl iodides and Zn Cu couple affords aryl alkyl ketones via the formation of alkylzinc species from alkyl iodides followed by transmetallation and reductive elimination[380]. The Pd-catalyzed carbonylation of the diaryliodonium salts 516 under mild conditions in the presence of Zn affords ketones 517 via phenylzinc. The a-diketone 518 is formed as a byproduct[381],... 

Triflates are used for the reaction[470]. The 5-phenyltropone 609 is prepared by coupling of the triflate with phenylzinc chloride[471]. Instead of the expensive triflale, phenyl fluoroalkanesulfonate as a triflate equivalent is used for coupling[472]. Phenyl fluorosulfonate (610) is another reagent used for cou-pling[473]. 

In the reaction of the 1,1-dichloro-l-alkene 611 with phenylzinc chloride, only monoarylation takes place regioselectively to give the (Z)-l-chloro-l-phe-nylalkene 612[468,474],... 

Diketene (635) is converted into 3-phenyl-3-butenoic acid (636) by the reaction of phenylzinc, magnesium, and aluminum reagents via C—O bond clea-vage[495j. 

The reaction of phenylzinc reagent proceeds with opposite stereochemistry, namely by retention of configuration at the final step via transmetallation. Both the (S)-( )- and (i )-(Z)-allylic acetates 4 and 9 afford the (/ )-( )-phe-nylated product II by overall inversion[23]. 

Fn some cases, r-allylpalladium complex formation by retention syn attack) has been observed. The reaction of the cyclic allyiic chloride 33 with Pd(0) affords the 7r-allylpalladium chlorides 34 and 35 by retention or inversion depending on the solvents and Pd species. For example, retention is observed in benzene, THF, or dichloromethane with Pd2(dba)3. However, the complex formation proceeds by inversion in these solvents with Pd(Ph3P)4, whereas in MeCN and DMSO it is always inversion[33]. The syn attack in this case may be due to coordination of Pd to chlorine in 33, because Pd is halophilic. The definite syn attack in complex formation has been observed using stereoche-mically biased substrates. The reaction of the cxoallylic diphenylphosphino-acetate 36 with phenylzinc proceeds smoothly to give 37. The reaction can be explained by complex formation by a syn mechanism[31]. However, these syn attacks are exceptional, and normally anti attack dominates. 

The allylic esters 189 and 191 conjugated with cyclopropane undergo regio-selective reactions without opening the cyclopropane ring. The soft carbon nucleophiles are introduced at the terminal carbon to give 190, and phenylation with phenylzinc chloride takes place on the cyclopropane ring to form 192[120]. 

A bis(secondary/tertiary) ligand reacted with diphenylzinc to afford the bis(phenylzinc) complex 88 (Scheme 67).148 The unusual reactivity of this dinuclear species was demonstrated by its interactions with trimethylphosphine oxide and iV,A-dimethylacetamide. In both cases, the products contained eight-membered rings incorporating both zinc atoms the structure of the bis(trimethylphosphine oxide) product is shown in Figure 46. 

Recently, a new method for synthesis of tertiary amines 326 from iV,iV-dialkyl O-benzoyl hydroxylamines 325 was proposed.425 The protocol is based on the copper-catalyzed reaction of hydroxylamines 325 with dialkyl- and diarylzinc reagents (Scheme 166). It is noteworthy that alkyl- and phenylzinc halides also reacted with compounds 325, however, yields were significantly lower than those for ZnR2 (18-29% vs. 69-98%). 

The catalytic asymmetric synthesis of allenes was first achieved by Elsevier and co-workers in 1989 [104]. A palladium-catalyzed cross-coupling reaction of an allenyl-metal compound 250 (M = ZnCl, MgCl or Cu) with iodobenzene in the presence of DIOP 251 gave 252 in 25% ee (Scheme 4.65). The synthesis of 252 by the reaction of 250 (M = Br) with phenylzinc chloride in the presence of a chiral palladium catalyst gave a quantitative conversion but very low enantiomeric excesses (3-9% ee). 

Berman and Johnson observed that amination of phenylzinc halide and n-butylzinc chloride with A-benzoyloxymorphoUne 2a and A,A-dibenzyl O-benzoyl hydroxylamine 2f, respectively, under Cu catalysis was not effective (equation 7) . 

They tried Ni catalysts with chelating amine and phosphine ligands in the reaction of phenylzinc bromide with A-benzoyloxymorpholine 2a and observed that in the presence of NiCl2(PPh3)2, n-alkyl, aryl and functionalized arylzinc chlorides can be aminated with A,A-disubstituted O-benzoylhydroxylamines in good yields (Schemes 20 and 21). Attempted amination of secondary and tertiary alkylzinc chlorides failed to yield the expected product. 

Theuseof DMPU (l,3-dimethyl-3,4,5,6-tetrahydro-2(l//)-pyrimidmone) as acosolvent in THF has been reported to increase the amination yield of arylzinc chlorides with Erdik and Omiir also reported competitive kinetic studies for the amination of substituted phenylmagnesium bromides and CuCN-catalyzed phenylzinc chlorides with acetone 0-(mesitylenesulfonyl)oxime 6f in THF and analyzed the rate data via the Hammett... 

Fig. 2.1.2.1 Reaction profile of the phenylzinc addition to p-chlorobenzaldehyde 37a, as determined by FT-IR. Curve A ZnPh2 (0.65 equiv), ZnEt2 (1.3 equiv), toluene, rt. Curve B ZnPh2 (1.50 equiv), toluene, rt.

Obviously, this rhodium-catalyzed diarylmethanol formation with boronic acids still requires significant optimization in order to be competitive with the forementioned existing methodology using phenylzinc reagents, but these early results appear particularly promising. 

These highly enantioselective Lewis-acid/Lewis-base-catalyzed dialkylzinc and phenylzinc addition reactions to imines give rise to arylalkylamides and diaryl-methylamides in excellent yields and enantioselectivities. Due to the simplicity of the process and the good availability of the imine precursors 23 from the corresponding aldehydes, wide applicability of the reported catalytic reaction can be expected. 

Also, the structures of two organozinc pivaloylacetone derivatives associated with methylzinc methoxide or phenylzinc phenoxide were determined by X-ray crystallography. The complex structures of these compounds, Et2Zn4(Pac)4(OMe)2 (175) and Ph2Zn4(Pac)4(OPh)2 (176) (Pac = pivaloylacetone anion), are shown schematically in Figure 87. 

O-propargyl-2-iodophenol in the presence of a palladium catalyst and phenylzinc chloride (3.30.) led to the formation of the 3-alkylidenedihydrobenzofurane in good yield (c.f 3.26.),37 The use of norbomene as capture reagent under similar conditions led to the formation of benzofurane bearing a tetracyclic hydrocarbon substituent.38... 

A 1,3-substituted allene, which has axial chirality instead of carbon central chirality, has been prepared by a palladium-catalyzed cross-coupling of 4,4-dimethylpenta-l,2-dienylzinc chloride (83) with phenyl iodide (5c) or by that of l-bromo-4,4-dimethylpenta- 1,2-diene (84) with phenylzinc chloride [60] (Scheme 8F.20). The highest enantiomeric purity (25% ee) of the allene (S)-85 was obtained in the former combination with (f ,/ )-diop (1) as chiral ligand. It is interesting that the enantiomeric purity was independent of the ratio of the reagents though the reaction seems to involve a kinetic resolution of the racemic 83. 

Alkylation of dihydropyranylacetates. The Pd(0)-catalyzed alkylation of allylic acetates by stabilized carbanions originally reported by Trost and Verhoeven (8,475 9, 451 -457)4 has been extended to alkylation of dihydropyranyl acetates as a route to natural C-glycopyranosides.5 Again the displacement is regioselective and results in net retention of configuration in reactions with most carbanions. However, alkylation with phenylzinc chloride or vinylzinc chloride occurs with inversion. 

Substituent effects on the rate of electrophilic amination of phenylmagnesium bromides, magnesium diphenylcuprates, and catalytic phenylzinc cyanocuprates with O-methylhydroxylamine in THF have been investigated in a competitive kinetic study.169 The mechanistic differences between these three reactions were discussed on the basis of the experimental results. 

Heck intramolecular cyclization. Silver carbonate or nitrate was added originally to tandem Heck arylation reactions to depress alkene isomerization, but they also improve selectivity in the -elimination step. Grigg et al.1 have used a number of useful additives such as triethylammonium chloride, sodium formate (15, 248), phenylzinc chloride, as well as silver(l) and thallium(I) salts. In fact, thallium(I) salts... 

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