Zinc mediated coupling

A preparative method involves zinc-mediated coupling of allyl halides with BUjSnCl in liquid ammonia. ... 

Copper-zinc mediated coupling of vinyl halides with alkyl or aryl iodides. 

From 1972 to 1975, Syntex synthesised the drugbybromination of2-naph-thol. The labile bromine atom at C-1 was removed with sodium bisulfite. After methylation of the naphthol came a zinc-mediated coupling reaction. The enantiomers were separated as before with cinchonidine. 

Allylstannanes result from stannylcupration of allenes, zinc mediated coupling of allylBr... 

On the other hand, zinc-mediated coupling of aldehydes to propargyl bromides in the Luche conditions gave the corresponding homopropargylic alcohols in moderate to high yields together with small amounts of a-allenic alcohols (Yavari and Riazi-Kermani, 1995). 

Carofiglio, T. Marton, D. Tagliavini, G. (1992) New simple route to allylstannanes by zinc-mediated coupling of allyl bromides with BuaSnCl or Bu2SnCl2 in an H2O (NH4C1)/THF medium, Organometallics, 11,2961-3. 

Marton, D. Russo, V. Stivanello, D. Tagliavini, G. (1996b) Preparation of benzylstannanes by zinc-mediated coupling of benzylbromides with organotin derivatives. Physicochemical characterization and crystal structures, Organometallics, 15,1645-50. 

The methodology used for the preparation of a Co-C(j/> ) bond for dienyl cobalt complexes (see below the Diels-Alder reactions in Section 7.01.3.5.4(i)) has been applied for the preparation of alkenylcobaloxime complexes 132 and 133 (Scheme 19). The methodology involved a zinc-mediated coupling of alkenyl halides and trifluoromethanes to (pyr)2(dmgH)2-Co 131 (pyr = pyridine dmgH = dimethylglyoximate). ... 

Table 16.1 Ligand effects on zinc-mediated coupling.

Several authors developed the method further of Ni(0)-mediated couplings to generate several PPP derivatives (9, 13, 14. They described homocouplings of various 1,4-dihalobcnzene derivatives by means of nickel(lI)chloridc/triphenylpho-sphine/zinc or the niekel(0)/cyclooctadiene complex. 

The couphng of N-substituted benzaldimines, mediated by the zinc-copper couple in the presence of (+)-camphorsulfonic acid (CSA) in DMF, was investigated. The best results were obtained for the imine 22, and the optimal balance of yield, diastereoselectivity and enantioselectivity for the diamine 23 was obtained using 3equiv of (+)-CSA [17] (Schemes). How-... 

A zinc-mediated carbon-carbon coupling reaction can be carried out on the metallated form of (t-butyldimethylsilyl)(2-pyridylmethyl)amine, formed in reaction with dimethylzinc. The isolated dimeric species can be reacted with further dimethyl zinc to give bis(methylzinc)-l,2-dipyridyl-l,2-bis(t-butyldimethylsilylamido)ethane, which contains two N3C coordinated zinc centers.89... 

Palladium-catalyzed alkenylation reactions involving pyrimidines can be achieved with hydrozirconated terminal alkynes, although the reaction is carried out in the presence of zinc chloride, so transmetallation to the zinc species is presumed to occur prior to the palladium-mediated coupling <1996ACS914, B-2002MI409>. Selective reaction at the 4-position of both 2,4-dichloropyrimidine and 2,4-dichloroquinazoline can be achieved. 

Despite the lower reactivity of solvated perfluoroalkylzinc reagents, perfluoroalkyl iodides undergo synthetically useful zinc-mediated reactions under Barbier conditions which often employ ultrasound and co-catalysts. Under these conditions, the zinc reagents are not well characterized and radical intermediates and SET mechanisms are proposed in some cases. Representative examples are presented below and include the ultrasound-promoted, zinc-mediated perfluoroalkylation of various substrates as reported by Ishikawa and coworkers (Scheme 10)123 126. Yields of carbinols could be improved by use of Ti(II) co-catalyst. Ultrasound promoted the coupling of perfluoroalkyl iodides with vinyl and allyl halides in the presence of Pd co-catalysts. 

Preparation of dioctylzinc by iodine-zinc exchange and its copper-mediated coupling with an electrophile preparation of ethyl 2-nonylacrylate... 

In diethyl ether, the yields of the zinc-mediated Barbier condensation are medium or poor,1 and THF should be preferred for most of the synthetic uses. Sonication is frequently used, e.g. in the reaction of methallyl bromide and salicylaldehyde which provide the expected alcohol27 The condensation of 4-bromo-2-sulfolene with a series of aldehydes and ketones was effected with the zinc-silver couple and ultrasound.28 The reaction occurs without transposition, which is not the case in the presence of magnesium. In refluxing... 

The zinc-mediated Reformatsky reaction is one of the classical methods for carbon-carbon bond formation. To date, various main group metals and transition metals have been used for this reaction. Rieke s activated indium powder mediates readily the coupling of ethyl a-bromoacetate and a variety of carbonyl compounds yielding /3-hydroxy esters in good yields (Scheme 87).3 Later, commercially available indium powder has been found to be equally effective for the indium-based Reformatsky reaction in THF.28 This indium Reformatsky reaction is accelerated by ultrasound irradiation (Scheme 88).322,323 Indium(i) iodide also mediates the Reformatsky reaction of aldehydes and ketones to give /3-hydroxy esters, presumably via organoindium(m) diiodide (Scheme 89).27... 

In a related procedure, the Diels-Alder substrate (118) was prepared from the iodide (117) through reductive metallation with a zinc-copper couple followed by palladium-catalyzed acylation (Scheme 49). This was a very rapid acylation in contrast to the related organotin-mediated coupling. 

In another metal-mediated coupling reaction, the highly functionalized dienes 136a and 136b were allowed to react with Ni(PPh3)4 in the presence of excess zinc/copper couple at 50 ""C and 1 atm of carbon monoxide to provide the octakis(methoxycarbonyl) 137a and the tetrabenzo derivatives 137b in excellent yields (77 and 84%, respectively), (see Scheme 17 compare also Scheme 12 for the formation of the related [4]radialene 10686-88) 373 s treated with excess LiBr H2O in HMPA at temperatures... 

---