Triflate elimination

It has been reported that (phenyl triflate)chromium complexes, even if electron rich, have a propensity to undergo anionic thia-Fries rearrangements in preference to triflate elimination (Scheme 99). ... 

Vinyl acetate reacts with the alkenyl triflate 65 at the /3-carbon to give the 1-acetoxy-1,3-diene 66[68]. However, the reaction of vinyl acetate with 5-iodo-pyrimidine affords 5-vinylpyrimidine with elimination of the acetoxy group[69]. Also stilbene (67) was obtained by the reaction of an excess of vinyl acetate with iodobenzene when interlamellar montmorillonite ethylsilyl-diphenylphosphine (L) palladium chloride was used as an active catalyst[70]. Commonly used PdCl2(Ph3P)2 does not give stilbene. 

An Q-arylalkanoate is prepared by the reaction of aryl halide or triflate with the ketene silyl acetal 74 as an alkene component. However, the reaction is explained by transmetallation of Ph - Pd—Br with 74 to generate the Pd eno-late 75, which gives the a-arylalkanoate by reductive elimination[76]. 

The aryl- and heteroarylfluorosilanes 541 can be used for the preparation of the unsymmetrical ketones 542[400], Carbonylation of aryl triflate with the siloxycyclopropane 543 affords the 7-keto ester 545. In this reaction, transme-tallation of the siloxycyclopropane 543 with acylpalladium and ring opening generate Pd homoenolate as an intermediate 544 without undergoing elimination of/3-hydrogen[401],... 

Hydrogenolysis of aryl and alkenyl halides and triflates proceeds by the treatment with various hydride sources. The reaction can be explained by the transmetallation with hydride to form palladium hydride, which undergoes reductive elimination. Several boro hydrides are used for this purpose[680], Deuteration of aromatic rings is possible by the reaction of aryl chlorides with NaBD4681]. 

Tandem cyclization/3-substitution can be achieved starting with o-(trifluoro-acetamido)phenylacetylenes. Cyclization and coupling with cycloalkenyl trif-lates can be done with Pd(PPh3)4 as the catalyst[9]. The Pd presumably cycles between the (0) and (II) oxidation levels by oxidative addition with the triflate and the reductive elimination which completes the 3-alkenylation. The N-protecting group is removed by solvolysis under the reaction conditions, 3-Aryl groups can also be introduced using aryl iodides[9]. 

Indoles with carbocyclic halogen or triflate substituents are potential starting materials for vinylation, arylation and acylation via palladium-catalysed pro-cesses[l]. Indolylstannanes. indolylzinc halides and indolylboronic acids are also potential reactants. The principal type of substitution which is excluded from such coupling reactions is alkylation, since saturated alkyl groups tend to give elimination products in Pd-catalysed processes. 

An example of cleavage ol the sulfur-oxygen bond in trifluoromethane-sulfonic ester has been reported Tnfluororaethyl triflate reacts with neutral or anionic nucleophiles with elimination of carbonyl difluoride and formation of trifluoromethanesulfonyl fluoride [57] (equation 32) The mechanism of this reaction involves elimination of fluoride ion, which is a chain carrier in the substitution of fluorine for the trifluoromethoxy group... 

An interesting class ot covalent Inflates are vin l and ar>/ or heteroaryl Inflates Vinyl inflates are used for the direct solvolytic generation of vinyl cations and for the generation of unsaturated carbenes via the a-elimination process [66] A triflate ester of 2-hydroxypyridine can be used as a catalyst for the acylation of aromatic compounds with carboxylic acids [109] (equation 55)... 

This reaction is not a bona fide Heck reaction per se for two reasons (a) the starting material underwent a Hg Pd transmetallation first rather than the oxidative addition of an aryl halide or triflate to palladium(O) (b) instead of undergoing a elimination step to give an enone, transformation 134 136... 

Treatment of 8-azidomethylperhydropyrido[l,2-c]pyrimidin-l-one 157 with methyl triflate and catalytic hydrogenation of the azide group led to the formation of tricyclic guanidine derivative 158 (01JA8851). Hydroxy group of 149 was protected with methoxymethyl chloride, and the p-methoxybenzyl protecting group (PMB) was eliminated by treatment with DDQ. 

When the reaction between a-trifluoromethyl sulfone 286 and paraformaldehyde was carried out in the presence of potassium carbonate, the vinyl sulfone was obtained quantitatively upon elimination of triflate anion368. Such a deacylative methylenation was observed in the reaction between /J-ketosulfones 287 and 288 and paraformaldehyde3 69 3 71. 

Triflate anions, elimination of 639 Triflinates, rearrangement of 669 Triflones 669... 

Solvolyses of these cyclic vinyl triflates at 100 in 50% aqueous ethanol, buffered with triethylamine, lead exclusively to the corresponding cyclo-alkanones. Treatment of 176 with buffered CH3COOD gave a mixture of cyclohexanone (85%) and 1-cyclohexenyl acetate (15%). Mass spectral analysis of this cyclohexanone product showed that the amount of deuterium incorporation was identical to that amount observed when cyclohexanone was treated with CH3COOD under the same conditions. This result rules out an addition-elimination mechanism, at least in the case of 174, and since concerted elimination is highly unlikely in small ring systems, it suggests a unimolecular ionization and formation of a vinyl cation intermediate in the solvolysis of cyclic triflates (170). The observed solvent m values, 174 m =. 64 175 m =. 66 and 16 m =. 16, are in accord with a unimolecular solvolysis. 

As indicated in this Scheme, triflate 184 presumably ionizes to vinyl cation 185, which can eliminate a proton and give acetylene 187 or react with solvent to give pinacolone 188 it can also undergo a methyl migration to give the tertiary... 

A very simplified but general scheme for the mechanism of all these transformations is shown below (Scheme 6.1). The first step of the catalytic cycle is the oxidative addition of the organo-hahde or -triflate B to produce the species C. Transmetallation of the appropriate organometalhc reagent D forms E which, upon reductive elimination, provides the desired product and regenerates the catalyst A. 

Transformations through 1,2-addition to a formal PN double bond within the delocalized rc-electron system have been reported for the benzo-l,3,2-diazaphospholes 5 which are readily produced by thermally induced depolymerization of tetramers 6 [13] (Scheme 2). The monomers react further with mono- or difunctional acyl chlorides to give 2-chloro-l,3,2-diazaphospholenes with exocyclic amide functionalities at one nitrogen atom [34], Similar reactions of 6 with methyl triflate were found to proceed even at room temperature to give l-methyl-3-alkyl-benzo-l,3,2-diazaphospholenium triflates [35, 36], The reported butyl halide elimination from NHP precursor 13 to generate 1,3,2-diazaphosphole 14 upon heating to 250°C and the subsequent amine addition to furnish 15 (Scheme 5) illustrates another example of the reversibility of addition-elimination reactions [37],... 

Thioacetals eliminate to vinylsulfides in the presence of CuOTf (Scheme 46).192 Cu1 and Cu11 triflates are mild Lewis acids for Friedel-Crafts acylation and alkylation reactions. CuOTf effectively catalyzes the reaction of anisole with selenoesters.193,194 Copper(II) sulfate promotes epoxide ring opening reactions in the presence of pyridine,195 with retention of configuration being observed. Cu(OTf)2 is a catalyst for the ring opening of aziridine by aniline.196... 

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