Diorganozinc Compounds Research Articles

Mechanochemical and slow-chemistry radical transformations: a case of diorganozinc compounds and TEMPO.

From the green chemistry perspective, molecular solid-state transformations conducted under mild conditions are of great interest and desirability. However, research in this area lacked popularity in the previous century, and thus progressed slowly. In particular, the application of radical reactions in solid-state chemistry has been hampered by several long-standing challenges that are intrinsically associated with the apparent unpredictable nature of radical chemistry. We present a comparative study of model mechanochemical, slow-chemistry and solution radical reactions between TEMPO and homoleptic organozinc compounds (i.e., di-tert-butylzinc and diphenylzinc). In the case of the tBu2Zn/TEMPO reaction system only a dimeric diamagnetic complex [tBuZn(μ-TEMPO*)]2 is obtained in yields slightly varying with the method chosen. In contrast, when TEMPO is mixed with diphenylzinc in a 2 : 1 molar ratio a novel paramagnetic Lewis acid-base adduct [[Ph2Zn(η1-TEMPO)]·TEMPO] is isolated in high yields regardless of the applied methodology. This adduct is also formed in the slow-chemistry process when TEMPO is gently mixed with Ph2Zn in a 1 : 1 molar ratio and left for two weeks at ambient temperature. Within the next week the reaction mixture gives in high yield a diamagnetic dinuclear compound [PhZn(μ-TEMPO*)][PhZn(μ2-η1:η1-TEMPO*)] and biphenyl. The analogous reaction conducted in toluene results in a much lower conversion rate. The reported results open up a new horizon in molecular solid-state radical transformations.

Addition of Mixed (Alkenyl)dialkylzincates to Vicinal Diketo Esters

Methods for the regioselective alkylation, arylation, and alkenylation of α,β‐diketo esters using organozinc reagents are reported. Alkylation and arylation at the α‐position is possible using diorganozinc compounds. Alkenylation can be achieved using mixed (alkenyl)dineopentylzincates.

ChemInform Abstract: Enantioselective Dialkylzinc‐Mediated Alkynylation, Arylation and Alkenylation of Carbonyl Groups

AbstractReview: 304 refs.

Regio‐ and Stereoselective Conjugate Addition of Aldehydes to β‐Tosyl Enones under the Catalysis of a Binaphthyl‐Modified Chiral Amine

AbstractA simple axially chiral amine catalyst promoted the regio‐, diastereo‐, and enantioselective conjugate addition of aldehydes to β‐tosyl enones, which serve as ynone surrogates. The adducts were readily converted by treatment with L‐selectride into less accessible enones with a γ stereogenic center. Such compounds cannot be prepared through the amine‐catalyzed conjugate addition of aldehydes to ynones. The obtained enones underwent further conjugate addition of diorganozinc compounds in the presence of a copper catalyst.

Regio- and Stereoselective Conjugate Addition of Aldehydes to β-Tosyl Enones under the Catalysis of a Binaphthyl-Modified Chiral Amine.

A simple axially chiral amine catalyst promoted the regio-, diastereo-, and enantioselective conjugate addition of aldehydes to β-tosyl enones, which serve as ynone surrogates. The adducts were readily converted by treatment with L-selectride into less accessible enones with a γ stereogenic center. Such compounds cannot be prepared through the amine-catalyzed conjugate addition of aldehydes to ynones. The obtained enones underwent further conjugate addition of diorganozinc compounds in the presence of a copper catalyst.

Dibenzyl and diallyl 2,6-bisiminopyridinezinc(ii) complexes: selective alkyl migration to the pyridine ring leads to remarkably stable dihydropyridinates

Diorganozinc compounds (ZnR2) with R = CH2Ph or CH2CH=CH2 react with 2,6-bisiminopyridines ((iPr)BIP) to afford thermally stable dihydropyridinate(-1) complexes, and do not react if R = CH2SiMe3 or CH2CMe2Ph. NMR studies reveal that dibenzylzinc binds (iPr)BIP at -80 °C, yielding the unstable complex [Zn(CH2Ph)2((iPr)BIP)]. Above -20 °C, this undergoes selective alkyl migration to the remote 4 position of the central pyridine ring.

Ni-Catalyzed Amination of Diorganozinc Compounds with N-Chloroamines

Ni-Catalyzed Amination of Diorganozinc Compounds with <i>N-</i>Chloroamines

A Strategy for C−H Activation of Pyridines: Direct C-2 Selective Alkenylation of Pyridines by Nickel/Lewis Acid Catalysis

The C-2 selective alkenylation of pyridine derivatives is achieved with a catalyst consisting of nickel and Lewis acid. Use of diorganozinc compounds as the Lewis acid catalyst gives C-2 monoalkenylation products, whereas AlMe3 changes the reaction course to afford C-2 dienylated products, which are derived from double insertion of alkynes into the C(2)−H bond. The reaction demonstrates a broad substrate scope and proceeds with high chemo-, regio-, and stereoselectivities under mild conditions compared with previous examples of direct C−H functionalization of pyridines.

Conjugate Addition of Organozinc Compounds to Nitroolefins

AbstractFor Abstract see ChemInform Abstract in Full Text.

Nucleophilic catalysis of the iodine-zinc exchange reaction: preparation of highly functionalized diaryl zinc compounds.

Sensitive functional groups are tolerated in an iodine–zinc exchange reaction catalyzed by Li(acac). Aryl and heteroaryl diorganozinc compounds with keto, aldehyde, or isothiocyanate substituents can be prepared by this method (see example in scheme; acac=acetylacetone, NMP=1-methyl-2-pyrrolidinone). Such zinc reagents serve as substrates for a wide variety of coupling reactions.

Conjugate Addition of Organozinc Compounds to Nitroolefins

Symmetrical (R2Zn) or mixed diorganozinc compounds (R1ZnR2) smoothly react with a series of nitroolefins in the presence of catalytic amounts of copper(I) salts and provide synthetically versatile nitro compounds in moderate to good yields. Simple alkyl groups, functionalized residues, or mixed trimethylsilylmethyl organozinc compounds (TMSM)ZnR may be employed for conjugate addition, while the TMSM group is not being transferred. ipso-Substitution is observed in absence of the copper(I) salt.

Conjugate Addition of Mixed Diorganozinc Compounds and Functionalized Organozinc Cuprates to Nitroolefins.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Conjugate Addition of Mixed Diorganozinc Compounds and Functionalized Organozinc Cuprates to Nitroolefins

[reaction: see text] The copper-catalyzed conjugate addition of symmetrical and mixed diorganozinc compounds as well as functionalized diorganozinc cuprates to nitroolefins leads to synthetically versatile nitro compounds in moderate to good yields. Mixed TMSM-organozinc compounds are suitable reagents for conjugate addition, since the TMSM group is not being transferred. Ipso substitution is observed in the absence of a catalytic amount of copper(I) salt. The nitroalkene moiety in 3-nitroacrylates proved to be the predominant Michael acceptor.

Formation of organozincate species from diorganozinc compounds and salts †

Stirring a benzene solution of a diorganozinc compound with an insoluble alkali metal alkoxide (MeOK or MeONa) or potassium amide (PhN(Me)K) formed a solution containing a species having a salt∶R2Zn composition of 1∶2. A salt (t-BuOK) that is soluble in benzene also forms a 1∶2 species and, when the salt to R2Zn ratio is sufficiently high, forms a 1∶1 species. Controlled heating at reduced pressure of solutions prepared from an alkali metal alkoxide and an excess of a diorganozinc compound leaves materials with alkoxide∶R2Zn ratios of 1∶2 or 1∶1. Reactions of benzene solutions of diorganozinc compounds with (p-MeC6H4)SK or Ph2PK form solutions of composition R3ZnK.

Stereoselective synthesis of secondary organozinc reagents and their reaction with heteroatomic electrophiles.

[figure: see text] Various trisubstituted olefins were converted to configurationally stable diorganozinc compounds with high diastereoselectivity. Their reaction with various electrophiles centered on tin, sulfur, bromine, and phosphorus provided the desired substitution products with retention of configuration. Novel, functionalized organocopper reagents such as 4 and chiral diphosphine 5 have been prepared.

Copper(I)-Catalyzed Enantioselective Substitution of Allyl Chlorides with Diorganozinc Compounds.

Ferrocenylamines are excellent catalysts for the enantioselective substitution of unsymmetrical allyl chlorides with dialkylzinc compounds in the presence of a copper(I) salt. For example, in the reaction shown in Equation (1), the product is formed with 87 % ee and a SN 2':SN 2 ratio of 97:3.

An Efficient Nickel-Catalyzed Cross-Coupling Between sp3 Carbon Centers.

Since the pioneering work of Wurtz, cross-couplings between sp3 carbon centers have had the reputation of being difficult. In the presence of a catalytic amount of m-trifluoromethylstyrene, an efficient cross-coupling reaction takes place between polyfunctional primary alkyl iodides and diorganozinc compounds [Eq. (a)] to give a general catalytic cross-coupling between sp3 carbon centers. Piv=pivaloyl; Pent = pentyl; acac = acetalacetonate; NMP = N-methylpyrrolidone.

An Efficient Nickel-Catalyzed Cross-Coupling Between sp3 Carbon Centers

Since the pioneering work of Wurtz, cross-couplings between sp3 carbon centers have had the reputation of being difficult. In the presence of a catalytic amount of m-trifluoromethylstyrene, an efficient cross-coupling reaction takes place between polyfunctional primary alkyl iodides and diorganozinc compounds [Eq. (a)] to give a general catalytic cross-coupling between sp3 carbon centers. Piv=pivaloyl; Pent = pentyl; acac = acetalacetonate; NMP = N-methylpyrrolidone.

β‐Silyl Diorganozinc Compounds—A New Class of Useful Zinc Reagents

β‐Silyl Diorganozinc Compounds—A New Class of Useful Zinc Reagents

The Role of Neutral and Radical Anionic Organozinc Complexes in the Alkylation Reactions of 1,4-Diaza-1,3-butadienes with Diorganozinc Compounds

We have earlier postulated the intermediacy of organozinc radical species in the regioselective alkylation reactions of 1,4-di-tert-butyl-1,4-diaza-1,3-butadiene (t-BuNCHCHN-t-Bu) with diorganozinc compounds (ZnR2). To verify these postulates, we have prepared and studied the neutral organozinc radical complex MeO(CH2)3Zn(t-BuNCHCHN-t-Bu) (A) and two diorganozinc radical-anionic complexes, K[R2Zn(t-BuNCHCHN-t-Bu)] (R = Me (8a), Et (8b)). A was prepared in situ by the reaction of t-BuNCHCHN-t-Bu with bis(methoxypropyl)zinc. Complexes 8 were prepared by reducing the 1:1 coordination complex ZnMe2(t-BuNCHCHN-t-Bu) (1a) with potassium or by the nucleophilic addition of K(t-BuNCHCHN-t-Bu) to ZnR2 (R = Me, Et). The resulting radical-anionic complexes are thermally unstable and readily undergo an intermolecular single-electron transfer, giving a mixture of the metallacyclic heteroleptic zincate complexes K[ZnR(t-BuNCHCHN-t-Bu)] (9) and K[ZnR(t-BuNC(R)CHN-t-Bu)] (10). The ratio in which the latter complexes are formed depends on the R group and on the concentration and the temperature. Alternatively, 9 has been prepared separately from the reduction of [ZnR(t-BuNCHCHN-t-Bu)]2 (4) with 2 equiv of potassium. The crystal structures of two complexes of 9, i.e. {9a(THF)}n and {9c(Et2O)1/2}n, have been determined. Both complexes form linear coordination polymers containing alternating potassium cations and zinc-diazabutadiene anions.