Vinylation, fluorous

Scheme 7.86 Vinylation of enamides employing fluorous ligands.

Unfortunately, the appeal of solid phase extractions on small scale fades as the scale increases due to the cost and inconvenience of using large amounts of fluorous silica gel. Here, modified techniques to reduce the tedium of repeated extractions are attractive. For example, Crich has recently introduced the minimally fluorous selenide C6Fi3CH2CH2C6H4SeH[171. This selenol is added in catalytic quantities to tin hydride reductions of reactive aryl and vinyl radicals. The high reducing capacity of the aryl selenide suppresses undesired reactions of product radicals without suppressing the reactions of the aryl and vinyl radicals themselves. After the reaction is complete, the selenol can be recovered by a modified continuous extraction procedure. 

A fluorous biphasic system has been used to reduce the metal contamination arising in the copper-catalysed living radical polymerization of vinyl monomers. 

Vinylic Oxidation. Various alkenes are oxidized to the corresponding ketones using fm-BuOOH in the presence of Pd(II) catalysts bearing perfluorinated ligands in a fluorous biphasic system.1309 The catalyst can be reused, but progressively longer reaction times are required. 

Free-radical-mediated four-component coupling reactions are rare. However, when an allyltin-mediated radical carbonylation is conducted in the presence of electron-deficient alkenes, four-component coupling reactions take place efficiently to give good yields of p-functionalized <5,fi-unsaturated ketones [40]. The wide scope of this four-component coupling reaction is noteworthy Primary, secondary, and tertiary alkyl bromides and iodides can be used as well as aromatic and vinylic halides. A variety of electron-deficient alkenes, such as methyl vinyl ketone, ethyl acrylate, acrolein, acrylonitrile, and vinyl sulfone, can be used as the acyl radical trap (Scheme 6.23). Fluorous allyltin compounds can also be used in four-component coupling reactions [41]. 

Fluorous organometallic chemistry, examples, 1, 842 Fluorous solubles, in organometallic synthesis, 1, 81 Fluorous solvents, for hydroformylations, 11, 450 Fluorous tin hydrides, preparation and applications, 9, 346 Fluorovinyl groups, vinylic C-F bond activation, 1, 753 Fluoro vinyltitanocenes, synthesis, 4, 546 g tfZ-Fluorovinyltributylstannane, in carbonylative cross-coupling, 11,413... 

Modified guanidines 3 efficiently catalyzed the asymmetric Michael addition of a prochiral glycine derivatives with acrylate, acrylonitrile and methyl vinyl ketone under simple and mild conditions. Remarkably, both product formation and enantioselectivity were dramatically improved using solvent-free conditions (Scheme 12) [34]. The addition of alcohols to methyl propiolate was performed using fluorous phosphines such as P[(CH2)2 (CF2)7 CF3]3 and again better yields of 99% have been obtained under solvent-free conditions. Toluene was added to efficiently separate the product from the solid catalyst, which was then reused without loss of activity [35],... 

Haney and Curran also studied the radical cychzation of vinyl iodide 10 in the presence of the fluorous tin hydride 14 (Scheme 4) [21]. After fluorous... 

Mcintee, J. W. and Valliant, J. F. (2007) Expanding the utility of the fluorous labeling method. Trialkylstannylation of functionalized aryl and vinyl halides with a fluorous distannane. J Labeled Comp. Radiopharm., 50, S198. 

The Sonogashira coupling reaction of terminal alkynes with aryl or vinyl halides is a useful tool for carbon—carbon bond formation, and has found wide employment in areas such as natural product synthesis, the pharmaceutical industry, and material sciences. Novel recyclable Pd catalysts with fluorous ponytails in the ligand 2,2 -bipyridine were reported in a copper-free Pd-catalyzed Sonogashira reaction in a fluorous biphasic system (FBS) (Equation 4.19). The catalysts are only soluble in perfluorinated solvents at room temperature [41],... 

Regioselective Heck vinylations of enamides have been studied under controlled microwave irradiation conditions using a palladium catalyst and fluorous bidentate... 

Scheme 16.66. Vinylation of enamides using fluorous ligands.

Studies on the controlled microwave-irradiated novel palladium-catalyzed reaction of a fluorous-tagged bidentate ligand (l,3-bis(diphenylphosphino) propane ligand, [F-dppp]) for regioselective Heck vinylations of enamides have... 

A highly fluorous alkoxy ethyl ether was synthesized and used as a protective group of alcohols. Treatment of an ether solution of 1 equivalent of a primary alcohol and 3 equivalents of the fluorous vinyl ether 29 with 5 mol% of camphorsulfonic acid (CS A) for 3 h at room temperature provided the desired protected alcohols 30 in 84-93% yields (Scheme 33). The products and the excess fluorous vinyl ether were extracted with FC-72 and then separated by column chromatography. Secondary and even tertiary alcohols were similarly protected in good yields in THF at 65°C for 30 5 min. The protected fluorous acetals were treated in a 1 1 solution of ether and methanol with 5 mol% of CSA for 1 h for deprotection. After completion of the reaction, the products were isolated in pure form by simple three-phase extraction (reaction mixture/saturated aqueous NaHC03/FC-72). 

Vallin, K.S.A, Zhang, Q.S., Larhed, M. et al. (2003) A new regioselective Heck vinylation with enamides. S3mthesis and investigation of fluorous-tagged bidentate ligands for fast separation. J. Org. Chem., 68, 6639 5. 

Another example of a radical reaction involves the addition of alkylthio radicals to alkenes using AIBN as a radical initiator. Equation 5 demonstrates the addition of fluorous thiol to vinyl silyl chloride to form fluorous functionalized silyl chloride in quantitative yield without forming polyaddition by-products. ... 

Fluorous reverse-phase silica gel (FRPSG)-supported Lewis acids are new and effective catalysts of Baeyer-Villiger and Diels-Alder reactions in water. FRPSG-supported Sc[C(S02C4F9)3]3 (5 mol%) catalyzes the Diels-Alder cycloaddition of 2,3-dimethyl-butadiene with methyl vinyl ketone in water at room temperature (16 h, 91%) and can be recycled by simple filtration after the reaction. ... 

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