Alkylzinc Iodides Research Articles

Iron‐Catalyzed Radical Zincations of Alkyl Iodides

AbstractWe report a new iron‐catalyzed I/Zn‐exchange allowing to convert primary or tailored secondary alkyl iodides into the corresponding alkylzinc iodides. In the presence of a remote double bond at position 5, diastereoselective ring closures are observed. Quenching of these zinc reagents, after transmetalation to copper species (with CuCN ⋅ 2LiCl) or under Pd‐catalysis, with typical electrophiles (allyl bromides, acid chlorides or aryl iodides) gave various polyfunctional products.magnified image

Stereoselective Synthesis of Cis- and Trans-Tetrasubstituted Vinyl Silanes Using a Silyl-Heck Strategy and Hiyama Conditions for Their Cross-Coupling.

We report a palladium-catalyzed, three-component carbosilylation reaction of internal symmetrical alkynes, silicon electrophiles, and primary alkyl zinc iodides. Depending on the choice of ligand, stereoselective synthesis of either cis- or trans-tetrasubstituted vinyl silanes is possible. We also demonstrate conditions for the Hiyama cross-coupling of these products to prepare geometrically defined tetrasubstituted alkenes.

Reaction of organozinc halides with aryl isocyanates

Reformatsky reagent, benzylzinc bromide or alkylzinc iodides react with aryl isocyanates directly to give corresponding N-substituted carbamates under mild reaction conditions. However, the reaction of allylzinc bromide or propargylzinc bromide with aryl isocyanates produces the corresponding N-substituted amides. The reactions provide alternative methods for the synthesis of N-substituted carbamates or amides.

Highly Selective Reactions of Unbiased Alkenyl Halides and Alkylzinc Halides: Negishi-Plus Couplings

High yielding stereo- and chemoselective Pd-catalyzed cross-couplings in THF at room temperature of alkenyl iodides and bromides with primary and secondary alkyl zinc iodides have been developed with the aid of N-methyimidazole as the key additive.

Kinetic Studies on the Stability and Reactivity of β-Amino Alkylzinc Iodides Derived from Amino Acids

Beta-amino alkylzinc iodides are intrinsically unstable toward beta-elimination and protonation. The aim of this study was to determine the rates of these processes and also to understand how the reactivity of a range of beta-amino alkylzinc iodides in Negishi cross-coupling reactions is influenced by the presence of functional groups within the zinc reagent. Decomposition of beta-benzamido alkylzinc iodides occurs by protonation, and the first-order rate constant for the self-protonation of the carbon-zinc bond in reagent 4b was determined to be 5.2 x 10(-6) s(-1) (at 291 K). In contrast, the carbamate derivative 2 decomposes by a first-order elimination process. The homologous reagent 3, derived from glutamic acid, decomposes more quickly by beta-elimination, with a first-order rate constant of 24 x 10(-6) s(-1) (at 291 K). Reagents 23 and 25, in which the Boc group has been replaced with a trifluoroacetyl group, are more stable toward beta-elimination than the corresponding reagents 2 and 3, a striking outcome given that the trifluoroacetamido group is a better leaving group. Moreover, this replacement also changes the mechanism of the elimination to a second order process. Pseudo-second-order rate constants for the Negishi cross-coupling of reagents 2, 3, 23, and 25 with iodobenzene have been determined, revealing the higher reactivity of the glutamic acid-derived reagents 3 and 25. The main factor influencing reactivity, therefore, is determined to be the proximity of the ester group, rather than the nature of the nitrogen protecting group. Finally, beta-amino alkylzinc iodides 46-48 containing Weinreb amides have been prepared, rate constants for their decomposition through elimination determined, and their synthetic potential for the preparation of beta-amino ketones established.

Ionisation of the ZincIodine Bond of Alkylzinc Iodides in Dimethylformamide from Theory and Experiment

Sheep in wolves′ clothing? Quantum chemical calculations suggest that coordination of DMF to alkylzinc iodides can promote ionisation of the zinciodine bond leading to the formation of solvated alkylzinc cations, as depicted. Such cations can also be detected by ESI-MS measurements. This ionisation may be partly responsible for the compatibility of alkylzinc iodides with acidic protons, as well as the lower reactivity of alkylzinc halides towards electrophiles compared to dialkylzinc reagents. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2111/2008/z801313_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

ChemInform Abstract: Copper‐Mediated 1,4‐Conjugation Reaction of Functionalized Alkylzinc Iodides with Derivatives of β‐Nitrostyrene.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

A Practical Synthesis of Multifunctional Ketones Through the Fukuyama Coupling Reaction.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Intramolecular Carbozincation of Unactivated Alkenes Occurs through a Zinc Radical Transfer Mechanism

The cyclizations of a number of terminally unsaturated alkenyl zinc iodides to cyclopentylmethylzinc iodides, formerly believed to be nonradical in nature, have been revealed as radical chain cyclizations initiated by adventitious oxygen. Five cases are presented in which the published carbozincation cis/trans selectivities are essentially the same as those found for the cyclizations of the unsaturated alkyl iodide precursors of the alkylzinc iodides by the iodine atom transfer method at approximately the same temperatures. In addition, it has been found that one of the organozinc cyclizations does not occur in a system in which oxygen has been rigorously excluded. The combined findings strongly suggest that these organozinc cyclizations occur by a zinc radical transfer mechanism rather than by a conventional carbometallation that is thought to occur with the analogous organolithium and organomagnesium cyclizations.

Copper-mediated 1,4-conjugation reaction of functionalized alkylzinc iodides with derivatives of β-nitrostyrene

Functionalized alkylzinc iodides will undergo 1,4-conjugation reaction with derivatives of β-nitrostyrene in the presence of Cu(OAc) 2/LiCl to afford a polyfunctional nitro-compound in high yield.

A Practical Synthesis of Multifunctional Ketones through the Fukuyama Coupling Reaction

AbstractA highly efficient, robust and scalable protocol for the synthesis of multifunctional ketones through Fukuyama coupling, i.e., cross‐coupling of thiol esters with zinc reagents, has been developed. Treatment of thiol esters with alkylzinc iodides or dialkyl zincs in the presence of palladium on activated carbon (Pd/C) or palladium acetate [Pd(OAc)2] furnished the corresponding ketones in high yields. Evaluation of the properties‐activities relationship of the Pd/C‐catalyzed reaction has proven that oxidic Pd/C is much more potent than reduced Pd/C in the reaction of thiolactone 1a with zinc reagent 2a. Based on the dependence of the Pd/C‐catalyzed reaction on the nature of Pd/C in combination with the extent of the Pd leaching from Pd/C to the solution, a dual reaction mechanism for the Pd/C‐catalyzed Fukuyama coupling reaction, which includes heterogeneous and homogeneous catalytic cycles, was proposed. The marked reduction of the zinc reagents and the use of Pd(OAc)2 in much smaller amounts were achieved when zinc bromide was added. This supports a hypothesis where a shift of the Schlenk equilibrium from inactive dialkylzincs (R2Zn) to active organozinc species, such as alkylzinc halides (RZnX) and three‐coordinate species [(RZnX2)−⋅ (ZnX)+], and generation of the stabilized monomeric Pd complexes during the reaction, may facilitate the reaction.

RZnI vs. R2Zn in Pd(0)-catalyzed cross-coupling reactions with thioimidates

Thioimidates 1-Z undergo facile cross-coupling with Pd(0)–RZnI but are inert to Pd(0)–R2Zn. This difference is due to the lower Lewis acidity of R2Zn, as opposed to lower nucleophilicity. Various sources of RZnI (R = Me, Et) and Pd(0) were evaluated for their convenience and reactivity.Key words: thioimidates, cross-coupling, dialkylzincs, alkylzinc iodides.

Nickel-catalyzed cross-coupling between functionalized primary or secondary alkylzinc halides and primary alkyl halides.

In the presence of Bu(4)NI (3 equiv) and 4-fluorostyrene (20 mol %), unreactive primary and secondary alkylzinc iodides undergo nickel-catalyzed cross-couplings with various primary alkyl iodides or bromides. More reactive secondary dialkylzincs and the mixed zinc organometallics RZnTMSM undergo the cross-coupling reaction in the absence of Bu(4)NI. The bicyclic secondary diorganozinc 6 prepared via boron-zinc exchange reacts with high retention of configuration. Free NH-groups are tolerated in the cross-coupling allowing the synthesis of aminated products.

ChemInform Abstract: Improved Nickel-Catalyzed Cross-Coupling Reaction Conditions Between ortho-Substituted Aryl Iodides/Nonaflates and Alkylzinc Iodides in Solution and in the Solid-Phase.

Abstract ortho-Substituted aryl iodides and nonaflates undergo nickel-catalyzed cross-coupling reactions with functionalized alkylzinc iodides in the solid-phase as well as in solution providing high HPLC purities and good yields.

Improved Nickel-Catalyzed Cross-Coupling Reaction Conditions between ortho-Substituted Aryl Iodides/Nonaflates and Alkylzinc Iodides in Solution and in the Solid-Phase

ortho-Substituted aryl iodides and nonaflates undergo nickel-catalyzed cross-coupling reactions with functionalized alkylzinc iodides in the solid-phase as well as in solution providing high HPLC purities and good yields.

Regio- and Stereoselective Addition of Nucleophiles to 1-Phenoxycarbonyl-2,3-dihydropyridinium Salts

Several 2-alkyl-1-phenoxycarbonyl-Δ 3 -piperidines were prepared by the addition of alkylzinc iodides to dihydropyridinium salt (9). The treatment of 4-hydroxy-2-methyl-1-phenoxycarbonyl-1,2,3,4-tetrahydro- pyridine (12) with allyltrimethylsilane in the presence of a variety of Lewis acids was studied and found to give cis- and trans-2-6-dialkyl- Δ 3 -piperidines (14) and (15) in moderate to good yield. Among the Lewis acids studied, stannyl chloride gave the best yield with good stereoselectivity (84:16) favoring the cis-isomer (14). The analogous reaction of the 4-methoxy derivative (13) with organozinc reagents was examined and found to give the cis-isomers (17) as the major products

ChemInform Abstract: Palladium‐Catalyzed Coupling Reaction of N‐Heteroaryl Halides with Functionalized Alkylzinc Iodides.

Reaction d'Het-X avec l'iodure d'w-R alkylzinc (X=Br, Cl, I, R=Cl ou COOEt, alkyl=ethyl, propyl, butyl, Het=pyridyl-2 ou -3, dimethyl-2,6 pyridyl-4 ou dimethyl pyrimidinyl); obtention de Het-(CH 2 ) n -R

The addition of alkylzinc iodides to 1-(phenoxycarbonyl)-2,3-dihydropyridinium salts. A synthesis of 2-alkyl-Δ 3-piperidines.

Several 2-alkyl-1-(phenoxycarbonyl)-Δ 3-piperidines were prepared by the addition of alkylzinc iodides to 1-(phenoxycarbonyl)-2,3-dihydropyridinium salts.

The addition of alkylzinc iodides to 1-(phenoxycarbonyl)pyridinium salts

Several 1-(phenoxycarbonyl)-1,2-dihydropyridines were prepared by the addition of alkylzinc iodides to 1-(phenoxycarbonyl)pyridinium salts.