Vinyl trifiate

Ishiyama, T., Takagi, J., Kamon, A., Miyaura, N. Palladium-catalyzed cross-coupling reaction of bis(pinacolato)diboron with vinyl trifiates -substituted by a carbonyl group efficient synthesis of -boryl- -unsaturated carbonyl compounds and their synthetic utility. J. Organomet. Chem. 2003, 687, 284-290. 

Alkenyl halides and trifiates are easily carbonylated. Carbonylation of a-iodo enone 3 proceeded at 60 °C using Pd(OAc)2 and DPPP, and the ester 4 was obtained in 62% yield [6]. The lactam 5 was converted to the vinyl trifiate 6, which was carbonylated to afford the a, -unsaturated ester 7 [7], Carbonylation of the alkenyl iodide 8, possessing a labile peroxy group proceeded smoothly to give the a, -unsaturated ester 9 under 1 atm of CO at 60 °C in DMF. The peroxy group remained intact [8]. 

The phosphine or other ligand that is used to stabilise the palladium(O) catalyst can have a dramatic effect on the rate of the reaction. Both tri(2-furyl)phosphine and triphenylarsine can be used in place of the more normal triphenylphosphine in reactions where this ligand gives poor yields. Indeed, the protocol for the Stille reaction between vinyl trifiate 14 and organostannane 15 contained in this chapter (Protocol 2) is an excellent example of this. The reaction was originally reported not to proceed. However, with triphenylarsine, Roth and co-workers have obtained excellent yields under mild conditions, without the need for added LiCl. ... 

Formation of Allenes. Quinoline can be used as an acid scrubber in the preparation of allenes via vinyl trifiate intermediates. The elimination of trifluoromethanesulfonic acid in quinoline proceeds in good yield (eqs 11 and 12). ... 

Arcadi, A., Cacchi, S., Fabrizi, G. and Moro, L. (1999) Palladium-catalyzed cydocarbonylation of o-ethynylphenols and vinyl trifiates to form 3-alkylidene-2-coumaranones. European Journal of Organic Chemistry, 1137-1141. 

Conversion of phenols to trifiate esters followed by vinylation constitutes one of the few general methods for the direct substitution of a carbon unit for a phenolic hydroxyl. Relatively few examples are known, but high generality is easy to predict. 

The transformation that has come to be known as the Heck reaction is broadly defined as the palladium(O)-mediated coupling of an aryl or vinyl halide or triflate with an alkene. The basic mechanism for the Heck reaction of aryl halides or trifiates (as outlined in more detail in the Key Chemistry), involves initial oxidative addition of the chiral palladium(O) catalyst to afford a a-arylpalladium(II) complex. Coordination of an alkene and subsequent carbon-carbon bond formation by syn insertion provide a a-alkylpalladium(II) intermediate, which readily undergoes P-hydride elimination to release the alkene product. Finally, the hydridopalladium(II) complex has to be converted into the active palladium(O) catalyst to complete the catalytic cycle. 

Alkenyl trifluoromethanesulphonates (enol triflates) undergo Heck coupling with alkenes efficiently (equation i23) i. This reaction is a useful variation of the use of vinyl halides not only because they are easy to prepare from the corresponding carbonyl compounds, but also because yields are good, and the stereochemistry of the trifiate is largely maintained. 

It was also discovered that aryl and vinyl iodides, bromides, and trifiates participated efficientiy in cross-coupiing reactions with organostannanes when catalyzed by palladium-on-carbon in the presence of Cu(l) as cocatalyst.f... 

Overman and co-workers [75] prepared alkenyltins via a vinyl triflate/ditin coupling. Mitchell and Kwetkat developed a simple route to acyltrimethylstannanes [187], whereas Hitchcock et al. [ 188] carried out a three-component tandem coupling reaction by reacting a 2-pyridyl trifiate, aryl or heteroaryl bromides, and hexamethylditin with Pd(PPh3)4 in the presence of LiCl to give azabiaryls (Scheme 4-48). 

The original procedure involved the coupling of aryl bromides with secondary amines. However, since then the scope has been expanded to include substrates such as aryl iodides, chlorides, fluorides, trifiates, tosylates, nonafiates, iodonium salts, and even boronic acids. While the reaction has not been extensively utilized with vinyl or alkynyl substrates, it can be performed with various heteroaryl halides. Similarly, numerous types of nitrogen-containing coupling partners, including primary amines, imines, various azoles, lactams, and simple amides, can now be used in this reaction. 

Aryl chlorides typically do not react under these conditions. However, Miyaura has been able to extend the scope of this reaction to include aryl chlorides by changing the catalyst system to Pd(dba)2 and PCys and replacing pinacolborane with bis(pinacolato)diboron. Vinyl iodides and trifiates undergo borylation with pinacolborane under similar conditions in the presence of triphenylarsine (AsPEb) (eq 17). Benzylic halides react with pinacolborane in the presence of PdCl2, PPhs, and N,N-diisopropylethyl amine (eq 18). Borylation of allylic halides in the presence of Pt(dba)2, AsPhs, and EtsN leads to highly regio-and stereoselective allylboronates (eq 19). 

Andersson, C.M. and HaUberg, A. (1989) PaUadium-catal3 ed vinylation of alkyl vinyl ethers with enol trifiates. A convenient s3mthesis of 2-alkoxy 1,3-dienes. J. Org. Chem., 54, 1502 5. 

Another Mizoroki-Heck mechanistic study using ESI-MS was undertaken by Nilsson et al. [28]. In this case, the specific reaction is the microwave-assisted arylation of w-butyl vinyl ether (25), an electron-rich olefin, with aryl triflates in the presence of different palladium sources and with the addition of chelating ligands. Using aryl trifiates as electrophilic partners also generates cationic intermediates, which may be more easily detected by ESI-MS. Scheme 7.12 shows the reactions studied by ESI-MS in this methodological work. 

Two specific reactions were studied the arylation of n-butyl vinyl ether (25) with two different trifiates, 1-naphthyl triflate (26), and 4-cyanophenyl trifiate (27). The four catalytic systems studied were based on palladacycles 30 and 31, pincer complex 32, Pd(OAc)2 and polyurea encapsulated Pd EnCat30. The authors used dppp (l,3-bis(diphenylphosphino)propane) (33) and (2S,4S)-(-)-2,4-bis(diphenylpho-... 

The Stille reaction mechanism was also evaluated by Alvarez et al. at DFT-B3LYP level obtaining similar conclusions the open mechanism is favored when anionic ligands (i.e. triflate) are used, whereas the cyclic mechanism is favored for X = halides [92]. These authors also investigated the role of the additive LiCl in the Stille reactions of vinylbromide and vinyl triflate with trimethyl vinyl tin catalyzed by Pd(PMe3)2- According to their results, the added chloride anion drives the expected transmetalation step from the open one with trifiates to the cyclic mechanism in the presence of the additive. 

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