Vinyl tosylates

Vinyl tosylates (but not vinyl triflates) may also be prepared from the ditosylate derivatives of 1,2-diols.14... 

Perhaps little attention has been devoted to a disturbing report by Frydman and Mazur (1970) concerning, in general, the reactivity of vinyl tosylates which possess at least one /3-hydrogen and, in particular, that of the isomeric 1,2-diphenylvinyl tosylates (134). These compounds, when heated at temperatures of at least 100° or irradiated with a tungsten filament lamp, are converted into the /8-ketosulphone 135 and the mechanism is a free-radical one as indicated in Scheme 13. 

Ion pair return to positions more remote than the adjacent carbon is quite common with homoallyl-cyclopropylcarbinyl cations, cf. compounds (92)-(94)l05 lol Even the vinyl tosylate (96) is produced from either of the allenic isomers (95) and (97)108 In contrast, 5-norbornen-2-yl brosylate (98) does not yield any nortricyclyl brosylate (99) although scrambling of a deuterium label, (98a) (98b), is ca. 12 times faster than solvolysis109. ... 

Fang, X. Wu, Y.-M. Deng, J. Wang, S.-W. Synthesis of monofluorinated indolizines and their derivatives by the 1,3-dipolar reaction of A-ylides with fluorinated vinyl tosylates. Tetrahedron 2004, 60, 5487-5493. 

Vinyl tosylates are also used. Coupling of the vinyl tosylate 55 with an 1-alkyne afforded the enyne 56. Only the use of PdCl2(PPh3)2, Cul, and r-Pr2NH gave satisfactory results [38]. 

Classical monophosphines, such as PhsP and (2-tolyl)3P introduced to the Mizoroki-Heck reaction by Heck and coworkers [6-8] and Spencer [77], are likely to belong to this class. Thus, in the nontrivial Mizoroki-Heck reaction of vinyl tosylate 93 with methyl acrylate (94), a mixture of Pd(OAc)2 with PhjP (P/Pd = 3 1) produces a completely inactive system. Conversely, high yields of the desired product 95 are obtained either by portionwise addition of Pd(OAc)2 or by the use of Pd(OAc)2 and PhsP in a 1 1 or, even better, 1 0.9 ratio (Scheme 2.20) [150]. 

Figure 3.8 Mizoroki-Heck coupling with 1-tert-butyl vinyl tosylate involving a 1,2-migration of the alkenyl palladium(ll) intermediate.

Vinyl tosylates and mesylates are useful substitutes for vinyl triflates [29]. Despite being electron poor, almost complete a-selectivity was obtained using various vinylating substrates. Enol ethers and enamides worked equally well, although cyclic moieties (e.g. iV-vinyl pynolidin-2-one) were found to be unproductive (Figure 3.23). 

Figure 3.23 a-Selective Mizoroki-Heck vinylation using vinyl tosylate and mesylate derivatives as coupling partners with enamides and butyl vinyl ether. 

The solvolysis of vinyl tosylate i proceeds via an sp hybridized carbocation. The Grunwald-Winstein m value for this reaction was found to be small (0.62) for such an ionization reaction, indicating much less stabilization from the solvent than occurs in the ionization of f-butylchlor-ide. This small m value could be due to increased nucleophilic assistance, or stabilization of the carbocation by some other factor, making the role of the solvent less important. 

An Example of a Change in Mechanism in a Solvolysis Reaction Studied Using cr" 452 A Swain-Lupton Correlation for Tungsten-Bipyridine-Catalyzed Allylic Alkylation 453 Using Taft Parameters to Understand the Structures of Cobaloximes Vitamin 612 Mimics 455 The Use of the Schleyer Method to Determine the Extent of Nucleophilic Assistance in the Solvolysis of Aryl vinyl Tosylates 459... 

Fluoroindolizines are easily available via cycloaddition of fluorinated vinyl tosyl-ates and pyridinium ylides [24], Using p-substituted pyridinium ylides both isomers (6 and 8) were formed with clear predominance of 8-isomers. One product with... 

Although the vinyl tosylates and recently also the simple vinyl pivalates [231] have been shown to serve very well in metal-catalyzed coupling reactions, the vinyl bromides and iodides are still the most popular substrates in this process. 

In general, alkenyl tosylates displayed enhanced reactivity compared to the corresponding phosphates in the Negishi cross couplings. However, decomposition of the aryl vinyl tosylates required the employment of the more stable aryl vinyl phosphates. Due to the weak coordinating abilities of the phosphate an alkenylpal-ladium(II) chloride complex is presumably formed after the oxidative addition similarly to the complex generated from the corresponding tosylate electrophiles [4]. 

In the light of the results presented by the group of Jamison and our own discoveries regarding the palladium catalyzed reaction between aryl and vinyl tosylates and electron rich olefins vide supra, it was decided to investigate the nickel catalyzed arylation of electron rich olefins in more detail [30]. 

H3PO4 as an external reference. All solvents were dried over neutral alumina in a solvent system under a positive argon pressure. t-Butyl vinyl tosylate 14, [1] t-butyl vinyl bromide 36 [2] and o-tolyl vinyl-1-chloride 18 [3] were prepared from the parent ketone according to known procedures. o-Tolyl vinyl-2-chloride 44 were synthesized by a Hunsdiecker reaction starting from the o-tolyl acrylic acid [4]. Pd[P(o-tol)3l2 was prepared according to known procedures [5]. 

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