Cross-coupling reactions alkenyl-aryl

When the first electrophile was not a ketone or an aldehyde, as illustrated for the reaction of 276 with crotonyl chloride, the intermediate chelated alkenylmetal 278 could also be subjected to iodinolysis or palladium-catalyzed cross-coupling reactions with aryl and alkenyl iodides in the presence of a stoichiometric amount of CuBr as a promotor as well as a polar cosolvent such as IV, IV-di methyl acetamide (DMA) (equation 131)165 166. 

A variety of fluorinated alkenyl zinc reagents such as CF2=CFZnCl, CF2=CHZnCl, E and Z-RCF = CFZnCl have been prepared by the first method (Scheme 54). In the presence of palladium catalyst, these fluorinated alkenyl zinc reagents undergo cross-coupling reactions with aryl iodides, vinyl iodides, acid chlorides and 1-iodo-l-alkynes to give the corresponding fluorinated alkenyl derivatives [127, 146-153], which have been utilized in the synthesis of fluorinated codlemones [154]. Typical examples are outlined below (Scheme 55). 

Synthetic reactions involving activation of alkenyl- and arylsilanes by copper salts have also been reported. A copper-mediated system is effective in the cross-coupling reaction of aryl- and heteroarylsilanes with aryl halides under Pd-free conditions (Equation (13)).66 Alkenyl- and arylsilanes as well as alkynylsilanes undergo homocoupling in the presence of Cul and air.65,65a Functionalized alkenyl- and arylsilanes bearing a coordination site in the vicinity of silicon (e.g., 7) are easily activated by copper salts even at room temperature (Scheme 5).67,67l 67e 68 q-jle organocoppers such as 8 are useful for carbon-carbon bond-forming reaction with carbon electrophiles. 

Allyltrifluorosilanes undergo the cross-coupling reaction with aryl hahdes, an allyl acetate, or alkenyl tiiflates exclusively at the y-carlxin to give allylated products (Scheme The y-selectivity is noteworthy, because the cross-couphng reaction using other allylmet-als usually takes place via a-attack. 

Application of Pd-catalyzed cross-coupling to a-aIkynylation,F30 a-alkenylation, and a-arylationF3 of heteroaromatic a,/3-unsaturated carbonyl derivatives, such as 5-iodouracil derivatives, has been known since the early 1980s (Scheme 50). Although these reactions are formally related to the Pd-catalyzed a-substitution discussed herein, the robust aromatic nature of the heteroaromatic substrates makes the requirements for their a-substitution less demanding. These reactions should therefore be viewed as a class of cross-coupling reactions involving aryl halides rather than a-halo-a,jS-unsaturated carbonyl compounds. In most... 

Scheme 2.18 Suzuki-Miyaura cross-coupling reactions of aryl and alkenyl ethers.

Phenethylzinc(II) bromide (PhCH2CH2ZnBr) is widely used in homobenzyUc couplings with aryl halides and alkenyl halides to generate 1,5-dienes [35c, 219-221]. Homoalkenyl- and homopropargylzinc halides are also reported to react with aryl halides [35c, 222, 223]. Recent examples of Pd-catalyzed cross-coupling reactions with aryl or alkenyl halides are highlighted in Scheme 3.57. However, the use of alkynyl halides in these reactions does not appear to have been reported [18c]. 

Palladium-catalyzed cross-coupling reaction of aryl-, alkenyl-, and cyclopropyl-boronic acids with 4-trifluoromethanesulfonyloxycoiunarin provides the corresponding 4-substituted coumarins in 63-85% yields (Equation 39) [39]. 

The intramolecular hydrosilation of homopropargyl alcohols also proceeds in a 5-exo manner to form five-membered cyclic vinylsilanes exclusively. Subsequent oxidation affords a p hydroxy ketone (eq 6). The vinylsilane also undergoes a Pd-catalyzed cross-coupling reaction with aryl or alkenyl halides stereoselectively (eq 6). The intramolecular hydrosilation thus provides an efficient methodology for the regio- and/or stereoselective functionalization and carbon-carbon bond formation of the alkyne moiety in homopropargyl alcohol. 

Cobalt catalysts also promote the cross-coupling reaction of aryl halides, alkenyl halides, and allyl methyl ethers to yield arylmethyl-, allyl-, and homoallyltrimethylsilanes, respectively (eq 25). ... 

Transition Metal Promoted Coupling Reactions. In the presence of a Ni catalyst, the reagent undergoes cross-coupling reactions with aryl bromides (eq 4). Alkenyl iodides are stere-ospecifically converted to alkenylsilanes in the presence of a Pd catalyst (eq 5). 

Kang, S.K. Lee, H.W. Jang, S.B. Ho, P.S. (1996) Palladium-catalyzed cross-coupling reactions of aryl-iodonium, alkenyl-iodonium and alkynyl-iodonium salts and iodanes with terminal alkynes in aqueous-medium, Chem. Commun., 835-6. 

Alkenylsilanols or isopropoxysilanes have been recently used for cross-coupling reactions of aryl or alkenyl halides under mild conditions. The palladium-catalyzed reaction of silanols has been optimized in the presence of Pd(dba)2, but in some cases the use of dimer (1) gave better results.The reaction of (Z)-vinylsilanols with vinyl iodides led to (Z,Z)-diene derivatives in 68% yield (eq 84). The stereoselectivity of the reaction was found to he 92.4% in favor of the (Z,Z)-isomer. 

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