Cross-coupling alkynyl-aryl

Bromination of the enol ether product with two equivalents of bromine followed by dehydrobromination afforded the Z-bromoenol ether (Eq. 79) which could be converted to the zinc reagent and cross-coupled with aryl halides [242]. Dehydrobromination in the presence of thiophenol followed by bromination/dehydrobromination affords an enol thioether [243]. Oxidation to the sulfone, followed by exposure to triethylamine in ether, resulted in dehydrobromination to the unstable alkynyl sulfone which could be trapped with dienes in situ. Alternatively, dehydrobromination of the sulfide in the presence of allylic alcohols results in the formation of allyl vinyl ethers which undergo Claisen rearrangements [244]. Further oxidation followed by sulfoxide elimination results in highly unsaturated trifluoromethyl ketonic products (Eq. 80). 

Various aryl, alkenyl and even alkylborane reagents of different reactivity can be used for coupling with aryl, alkenyl, alkynyl and some alkyl halides, offering very useful synthetic methods. The cross-coupling of aryl and heteroarylboronic acids with aryl and heterocyclic halides and triflates provide useful synthetic routes to various aromatic and heteroaromatic derivatives. Sometimes, the reaction proceeds in the... 

A more general method for arylation of terminal alkynes as well as electron-deficient alkynes is the Negishi Pd-catalyzed cross-coupling of aryl halides with alkynyl-zinc reagents. When using functionally substituted alkynylzincs, the deprotonation of 1-alkynes must be done with LDA instead of alkylithiums. 

A coupling reaction that does not involve prior preparation of a Cu(I) acetylide is provided by Pd-catalyzed cross-coupling of aryl halides with acetylenes in the presence of Cul. The 4-alkynylated product (357) was obtained from the corresponding 4-iodo derivative in 84% yield using Pd-catalysis, and in 54% yield from preformed Cu(I) acetylide without catalysis [87ACSA(B)219]. 

The Negishi alkynylation reactions are most efficient in the context of C(sp)-C(sp ) cross-couplings. Reactive aryl or alkenyl iodides and chlorides are suitable electrophilic partners, as well as other related electrophiles such as triflates, acetates, or tosylates. Notably, 2-methylthiooxazole (302) is also a suitable partner that can be converted, for instance, into the corresponding 2-ethynyloxazole 303 in the presence of Pd(PPh3)4 in THF at 60 °C (Scheme 4.68) [202]. 

In an early example of this reaction aryl and benzyl zinc halides were coupled with aryl halides (equation 40) (102). Alkynyl zinc compounds cross-couple with aryl halides (iodides or bromides) in the presence of a Pd catalyst (equation 41) (103) or alkynyl iodides can be coupled with aryl and alkenyl zinc compounds (equation 42) (100). 

Alkyl- and aryl-pyridazines can be prepared by cross-coupling reactions between chloropyridazines and Grignard reagents in the presence of nickel-phosphine complexes as catalysts. Dichloro[l,2-bis(diphenylphosphino)propane]nickel is used for alkylation and dichloro[l,2-bis(diphenylphosphino)ethane]nickel for arylation (78CPB2550). 3-Alkynyl-pyridazines and their A-oxides are prepared from 3-chloropyridazines and their A-oxides and alkynes using a Pd(PPh3)Cl2-Cu complex and triethylamine (78H(9)1397). 

Palladium And/Or Copper-Mediated Cross-Coupling Reactions Between 1-Alkynes And Vinyl, Aryl, 1-Alkynyl, 1,2-Propadienyl, Propargyl And Allylic Halides Or Related Compounds. A Review, Rossi. R. Carpita, A. Beilina, F. Org. Prep. Proceed. Int., 1995, 27, 129... 

Carbonylative cross-coupling of various iodonium salts bearing transferable aryl, heteroaryl, alkenyl, alkynyl residues with phenylboronic acid takes place under mild conditions giving the respective ketones in high yields (Equation (16)). The yields of competing cross-coupling do not exceed 8%. 

---