Copper-catalyzed vinylations stereospecific

In recent years, cross-coupling methodology has emerged as a viable tool for enamide synthesis, and, indeed, there are a number of published protocols which employ palladium- or copper-catalyzed stereospecific amidations of vinyl halides [17]. For example, Buchwald and coworkers had recently shown that a copper-catalyzed cross-coupling of vinyl bromides or iodides proceeded with retention of stereochemistry (Scheme 9.16), though the only example using a tetrasubstituted vinyl halide, 23, lacked the need for any stereochemical control in the halide portion [18]. Based on this it seemed feasible that the desired enamide 22 could potentially be assembled via a comparable coupling between amide 24 and a stere-odefined vinyl halide such as 25. 

The copper-catalyzed stereospecific allylation of alkenylboranes with allyl bromides occurs in a facile manner for both disubstituted1 and trisubstituted double bonds (equation 37)50. Only very small amounts of incorporation of the borane alkyl group were observed, and apparently none of the vinyl homocoupling products competed. 

Allyl vinyl ethers may be prepared via stereospecific copper-catalyzed coupling of allyl alcohols and vinyl halides. For example, the copper catalyst derived from the tetramethyl 1,10-phenanthroline ligand shown below facilitates C-0 bond formation between ( )-vinyl iodides and allyl alcohols when the reaction mixture is heated in the presence of air. ... 

Copper(II) triflate has also been used for the carbenoid cyclopropanation reaction of simple olefins like cyclohexene, 2-methylpropene, cis- or rran.y-2-butene and norbomene with vinyldiazomethane 2 26,27). Although the yields were low (20-38 %), this catalyst is far superior to other copper salts and chelates except for copper(II) hexafluoroacetylaeetonate [Cu(hfacac)2], which exhibits similar efficiency. However, highly nucleophilic vinyl ethers, such as dihydropyran and dihydrofuran cannot be cyclopropanated as they rapidly polymerize on contact with Cu(OTf)2. With these substrates, copper(II) trifluoroacetate or copper(II) hexafluoroacetylaeetonate have to be used. The vinylcyclopropanation is stereospecific with cis- and rra s-2-butene. The 7-vinylbicyclo[4.1.0]heptanes formed from cyclohexene are obtained with the same exo/endo ratio in both the Cu(OTf)2 and Cu(hfacac)2 catalyzed reaction. The... 

The cross-metathesis of the allylic phosphonate (480) and hydroxyalkenes (481) using the second generation Grubbs catalyst (482) and copper(I) iodide afforded substituted allylic phosphonates (483) in good yields (Scheme 123). Further stereospecific palladium(0)-catalyzed cyclization gave tetrahydrofuran (n = 1) and tetrahydropyran (n = 2) vinyl phosphonates (484). ... 

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