Triflates elimination reactions

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],... 

Initially the Pd(0) complex oxidatively adds to enol triflate 6 to form a vinyl-Pd(II) species. Carbon monoxide then inserts into the new Pd—C o-bond to yield a palladium(ll)-acyl complex which captures methanol. The methanolysis step is formally a reductive elimination reaction in which the Pd(0) catalyst is regenerated to propagate the catalytic cycle (Scheme 6.8).7... 

In contrast, few examples of reductive elimination reactions that form the C-N bond in amines are known. Only in the past several years have complexes been isolated that undergo these reactions [49-54]. These reductive eliminations are the crucial C-N bond-forming step of the aryl halide and triflate amination chemistry discussed in this review. Information on how these reactions occur, and what types of complexes favor this process, has been crucial to the understanding and development of new amination catalysts [50],... 

Elimination reactions (cf. 982, Section 3.2.3.12.1.2). If salts like 1005 are heated in the absence of nucleophile, Ei elimination occurs thus, the pentacyclic triflates (1005 R = primary alkyl) decompose at 150C. The sec-alkyl analogues form alkenes even at 20 C. 

Cyclization of a-propargyl-/3-ketoesters can be combined with cross-coupling of aryl halides or triflates in an oxypalladation-reductive elimination reaction to yield arylfurylmethanes (Equation 12) <2003X4661 >. 

In the majority of substitution and elimination reactions, the sulfonate moiety functions as the leaving group, and certain sulfonates, e.g. methanesulfonate (mesylate), p-toluenesulfonate (tosylate) and trifluoromethanesulfonate (triflate), are exceptionally good leaving groups. The introduction of these sulfonate groups therefore greatly facilitate... 

Alkanesulfonyl chlorides can also react by an initial elimination in water, mesyl chloride hydrolyses below pH 6.7 by an S 2 reaction of water at sulfur, between pH 6.7 an 11.8 by capture of the sulfene by water and above pH 11.8 by capture of the sulfene with hydroxide ion. An extended study of mesylations of phenols catalysed by various pyridines revealed a competition between the sulfene pathway and a general base-catalysed attack of the phenol, which was dependent on the pAa of both phenol and pyridine, with no mention of an A-mesylpyridinium ion. However, formation of an A-triflylpyr-idinium ion occurs immediately pyridine and triffic anhydride are mixed and this is probably the triflating species. Reaction via an A-sulfonyl quaternary ammonium ion therefore becomes important with more basic amines and more electrophilic sulfonylating reagents. 

Formation of transient bicyclo[2.2.1]hept-2-en-5-yne from phenyl-(3-trimethylsilyl-bomadien-2-yl)iodonium triflate is a reality shown by trapping experiments." An unusual elimination reaction is involved in the generation of perfluoroalkylethylenes from l-iodo-l-trimethylsilyl-2-perfluoroalkylethanes." The substrates are available from radical addition of perfluoroalkyl iodides to vinyltrimethylsilanes. 

This elimination reaction has been applied to the adducts (2) obtained by reaction of lithio dithiophenoxymethane (1) with aldehydes or ketones. Treatment of (2) with cuprous triflate and a base gives the homologous a-thio-phenoxy ketone (3) with preferential migration either of hydrogen or of the more highly substituted alkyl group. 

In the presence of bulky X ligands, a facile methyl halide elimination reaction is observed (Eq. 2) [3]. In this elimination the siliconium ion complex 2, with its two N->Si dative bonds, is converted into a neutral pentacoordinate complex 3, with only one remaining dative bond (Fig. 1, Table 1). The reaction is probably driven by partial release of steric interaction, caused by the removal of one of the A-methyl groups. This is indicated by a decrease in elimination rate in the presence of less bulky ligands, cyclohexyl and isobutyl, and the failure to observe elimination when X = methyl. The reactivity order of the halide ions follows their nucleophilicities F > Br > CF, while the less nucleophilic triflate ion does not react at all. 

The preparation of the quinoline system by pericyclic reactions is less important than the previous syntheses. Some cyclization/elimination reactions of iV-phenylimines 95 and 96 with alkynes, enol ethers or enamines are of preparative interest. Although they correspond to [4+2] cycloadditions, they are likely to proceed by SeAt mechanisms and are usually catalysed by Lewis acids. In the enolether cycloaddition to imines 95 ytterbium(III)triflate proved to be particularly effective [104]. 

Conjugate addition-elimination reaction of nitromethane with p-trifloxy acrylate in the presence of TMG (3) was reported by Chung et al. [11]. Treatment of enol triflate 46 with nitromethane and DMPU as a co-solvent in the presence of TMG (3) gave allyl nitro compound 47 in 60-70% yield via a conjugate addition-ehmination process. In this... 

These palladium-catalysed reactions involve insertion of the palladium into the carbon-bromine or carbon-triflate bond, reaction with the organometallic species (alkenyl stannane in a Stille reaction, arylboronic acid in a Suzuki reaction, or alkynyl copper species in a Sonogashira reaction) and reductive elimination to give the products shown below. 

Elimination of Thiophenol from Thioacetals. Conversion of thioacetals to vinyl sulfides is accomplished under exceptionally mild conditions by treatment with (CuOTOa-CeHe (eq 45). The reaction involves an a-phenylthio carbocation intermediate. Three factors contribute to the effectiveness of this synthetic method the Lewis acidity of a copperfT) cation that is unencumbered by a strongly coordinated counter anion, the solubility of the copper(I) triflate-benzene complex, and the insolubility of CuSPh in the reaction mixture. An analogous elimination reaction provides an effective route to phenylthio enol ethers from ketones (eq 46). ... 

Cyano-glycal and 1-cyano-hydroxylglycal derivatives have been produced by elimination reactions applied to the products of photobromination of esterified glycosyl cyanides, the reagents used were, respectively, zinc, pyridine and mercury(II) cyanide in nitrobenzene in the presence of silver triflate. ... 

Ionic liquids (IL) can be used as solvents for nucleophilic substitution reactions of alkyl halides or tosylates with NaN3. ° The authors studied three ionic liquids (84 and 85), [bmim][PF6], [bmim][N(Tf)2]> [hpyr][N(Tf)2] (where bmim = l-butyl-3-methyl-imidazo-lium, hpyr = 1-hexylpyridinium, PFg = hexafluorophosphate, N(Tf)2 = bis(trifluoromethy lsulfonyl)imide). It was observed that nucleofugacity scales for this reaction are similar to those reported for the same process in cyclohexane. It was also observed that elimination reaction does not compete with substitution even in cases with sterically hindered substrates such as the triflate ester of diacetone-D-glucose 81. The nucleophilic displacement on n-octyl mesylate (86) with potassium azide in a biphase system of supercritical carbon dioxide (SCCO2) and water, in the presence of catalyst Bu4PBr is also an adequate medium for the synthesis of the corresponding azide 87 ° (Scheme 3.11). 

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]. 

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