Chlorides cross-coupling

Alkyne coupling reactions under Pd/Cu conditions have been extended to other functional groups. Allenes couple with alkynes without incident (equation 143)277, as do dithio-carbonyl chlorides and thiocarbamoyl chlorides278. Alkynyl chloride cross-couple with alkynes in at least some cases, to form diynes279. 

The stannane-acyl chloride cross-coupling has been directed towards access to 3-acylcyclobutenones and a-heterosubstituted ketones. ... 

In 1996, Hatanaka considerably expanded the scope of this process with [Pd(Pt-Pr3)202] as the catalyst in the presence of KF, estabhshing that a wide variety of electron-deficient aryl chlorides cross-couple with arylchlorosilanes (Equation 2.48) [87]. 

The ester 870 is prepared by the cross-coupling of the chloroformate 869 with an organotin reagent. Some chloroformates are easily decomposed by a Pd catalyst, and hence the reaction should be carried out by slow addition of the chloroformates. Similarly, the amide 872 is prepared by the reaction of the carbamoyl chloride 871 [742]. The coupling of alkylcopper with ethyl chloroformate catalyzed by Pd affords esters[743]. 

Organoboranes are reactive compounds for cross-coupling[277]. The synthesis of humulene (83) by the intramolecular cross-coupling of allylic bromide with alkenylborane is an example[278]. The reaction of vinyiborane with vinyl-oxirane (425) affords the homoallylic alcohol 426 by 1,2-addition as main products and the allylic alcohol 427 by 1,4-addition as a minor product[279]. Two phenyl groups in sodium tetraphenylborate (428) are used for the coupling with allylic acetate[280] or allyl chloride[33,28l]. 

The preparation of perfluoroalkylzinc compounds has been achieved earlier 111 ethereal solvents [26] However, solvent effects play a significant role in the course of this reaction When a mixture of acetic anhydride and methylene chloride is used, coupled and cross-coupled products can be formed [27, 28] (equations 19 and 20) However, the cross-coupling reaction often gives mixtures, a fact that seriously restricts the synthetic applicability of this reaction [27, 28, 29]... 

Optically active (Z)-l-substituted-2-alkenylsilanes are also available by asymmetric cross coupling, and similarly react with aldehydes in the presence of titanium(IV) chloride by an SE process in which the electrophile attacks the allylsilane double bond unit with respect to the leaving silyl group to form ( )-s)vr-products. However the enantiomeric excesses of these (Z)-allylsilanes tend to be lower than those of their ( )-isomers, and their reactions with aldehydes tend to be less stereoselective with more of the (E)-anti products being obtained74. 

Trimethyl(l-phenyl-2-propenyl)silane of high enantiomeric excess has also been prepared by asymmetric cross coupling, and reacts with aldehydes to give optically active products in the presence of titanium(IV) chloride. The stereoselectivity of these reactions is consistent with the antiperiplanar process previously outlined75. 

Scheme 21 RCM of vinyl chlorides and subsequent cross coupling [89b]...

The Suzuki reaction was also used to prepare the polyketone since this particular reaction tolerates the subsequent step (Scheme 6.19).135 Palladium-catalyzed cross-coupling of aromatic diacid chlorides and bis(trimethylstannane) monomers was utilized to prepare poly(arylene ether ketone)s.136... 

TABLE IRON CATALYZED CROSS COUPLING REACTIONS OF GRIGNARD REAGENTS WITH (HETEROJARYL CHLORIDES OR -TRIFLATES... 

Similarly, Kappe and Walla showed that (2-pyridinyl)zinc chloride can be quickly cross-coupled with electron-deficient aryl chlorides using Pd2(dba)3/ t-Bu3P.HBp4 as a precatalyst in THF at 175 °C for 10 min (Scheme 2) [21]. hi a reverse approach, 4-chloropyridine rapidly reacted with (4-methoxyphenyl) zinc chloride (Scheme 2). 

Diheteroaryl-l,l -binaphthyls were prepared from 2,2 -diiodo-l,T-binaphthyl via microwave assisted cross-coupling by Putala and Kappe using several heteroarylzinc chlorides (2-thienyl)zinc chloride, (2-furyl)zinc chloride, and (3-pyridinyl)zinc chloride (Scheme 3) [22]. Importantly, no racem-ization occurred at the reaction temperature used, giving access to (R)-2,2 -diheter0aryl-1,T-binaphthyls starting from (i )-2,2 -diiodo-l,l -binaphthyl in excellent yields in 1 to 5 min of microwave irradiation. 

FuNn iONAL Group Tolerance of PdildbrO VIMes.HCI Catalyzed Suzuki Cross-Coupling Reactions of Aryl Chlorides with Phenyi.boronic Acid Derivatives... 

A catalytic version of the coupling was also developed, by using 10 mol % of CuCl2 and 20 mol % of sparteine 1 (silver chloride was used as a stoichiometric oxidant to regenerate the copper (II) oxidant). This catalytic system was applied to the asymmetric cross-coupling leading to 101 in a 41% yield and 32% ee. 

In the context of NHC/metal catalysed cross-coupling reactions, the only example of a Hiyama reaction was reported by Nolan using an in situ protocol by mixing Pd(OAc)j and IPr HCl for the formation of the catalyst. Activated aryl bromides and chlorides, such as 2-chloropyridine, were coupled with phenyl and vinyl-trimethoxysilane in good yields [123] (Scheme 6.39). 

Kotschy et al. also reported a palladium/charcoal-catalyzed Sono-gashira reaction in aqueous media. In the presence of Pd/C, Cul, PPI13, and z -Pr2NH base, terminal alkynes smoothly reacted with aryl bromides or chlorides, such as 2-pyridyl chloride, 4-methylphenyl bromide, and so on, to give the expected alkyne products in dimethyl-acetamide (DMA)-H20 solvent. Wang et al. reported an efficient cross-coupling of terminal alkynes with aromatic iodides or bromides in the presence of palladium/charcoal, potassium fluoride, cuprous iodide, and triph-enylphosphine in aqueous media (THF/H20, v/v, 3/1) at 60°C.35 The palladium powder is easily recovered and is effective for six consecutive runs with no significant loss of catalytic activity. 

A palladium catalyst with a less electron-rich ligand, 2,2-dipyridyl-methylamine-based palladium complexes (4.2), is effective for coupling of aryl iodides or bromides with terminal alkynes in the presence of pyrrolidine and tetrabutylammonium acetate (TBAB) at 100°C in water.37 However, the reactions were shown to be faster in NMP solvent than in water under the reaction conditions. Palladium-phosphinous acid (POPd) was also reported as an effective catalyst for the Sonogashira cross-coupling reaction of aryl alkynes with aryl iodides, bromides, or chlorides in water (Eq. 4.18).38... 

Homocoupling of alkyl halides in aqueous media can be mediated by manganese/cupric chloride to give the dimerization products in good yield. Cross-coupling can also be controlled to give the desired... 

The generated palladium chlorides possessing phosphinous acid ligands were found to be remarkably active and efficient catalysts in the presence of bases for a variety of cross-coupling reactions of aryl halides with aiylboronic... 

In summary, these results demonstrate that air-stable POPd, POPdl and POPd2 complexes can be directly employed to mediate the rate-limiting oxidative addition of unactivated aryl chlorides in the presence of bases, and that such processes can be incorporated into efficient catalytic cycles for a variety of cross-coupling reactions. Noteworthy are the efficiency for unactivated aryl chlorides simplicity of use, low cost, air- and moisture-stability, and ready accessibility of these complexes. Additional applications of these air-stable palladium complexes for catalysis are currently under investigation. 

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