Organic zinc compounds contain carbon-zinc chemical bonds in organic chemistry. Organic zinc compounds are among the first organometallic compounds. Most organic zinc compounds are easily oxidized and decomposed when dissolved in protic solvents. All reactions using organozinc reagents need to be reacted in the absence of inert gas, such as nitrogen or argon. Organic zinc compounds can be classified according to the substituents bound to the metal. One is diorganozinc, a class of organic zinc compounds with two alkyl ligands. The second type is heteroleptic, which the electronegative or monoanionic ligands such as halides are attached to the zinc center with another alkyl or aryl substituent. The third type is ionic organic zinc compounds, and this class is divided into organozincates and organozinc cations.
Cross-coupling reaction: Organic zinc compound is an excellent reagent for transition metal-mediated processes. N-Tosylaziridine is used as the electrophilic component coupled to alkylzinc bromide. The first step is the oxidative addition of a low-valent nickel species to the C-N bond of aziridine. In the final step, transmetalation and reductive elimination completes the catalytic cycle. Arylation of α-CF3-substituted alkyl bromides is carried out by using aromatic organozinc reagents obtained from aryl lithium and zinc chloride. The reaction is catalyzed by nickel chloride and chiral bis-oxazoline ligand. It is noteworthy that racemic secondary bromides provide arylated products with excellent enantioselectivities.
Electrophilic reaction: Sulfur dioxide is a good electrophile for coupling with a polar organometallic. This reagent is used as an equivalent of SO2 in the reaction with organic zinc compound. The reaction can proceed at room temperature to give the sulfonate salt, which can be further converted to the sulfone by addition of dimethylsulfoxide co-solvent and alkylating agent. Organic zinc reagent can be coupled with 2,4,6-trichlorophenyl chlorosulphate and subsequently reacted with the amine providing the sulfonamide. After the first step, the substitution product is produced depending on the type of organozinc reagent.
Addition reaction: The reaction of the aryl isocyanate with the organozinc reagent provides different products according to the structure of organozinc reagent. Thus, the addition of allyl and propargylzinc bromide gives amides. In contrast, the reaction that benzyl and alkylzinc react with the same isocyanate under similar conditions gives about 60% yield of carbamates. The reason why the reactions happen is that trichloroacetyl isocyanate is particularly electrophilic owing to electron accepting trichloroacetyl moiety. It rapidly reacts with aryl and vinyl organozincs, and subsequent methanolysis affords primary amides.
Fig.1. Addition of organozinc nucleophiles to N-activated quinolines and isoquinolines.
1. Luzung M R.; et al. A Mild, Functional Group Tolerant Addition of Organozinc Nucleophiles to N-Activated Quinolines and Isoquinolines[J]. The Journal of organic chemistry, 2017, 82(19): 10715-10721.