Arylations 2- phenyl triflate

The reaction of a halide with 2-butene-1,4-diol (104) affords the aldehyde 105, which is converted into the 4-substituted 2-hydroxytetrahydrofuran 106, and oxidized to the 3-aryl-7-butyrolactone 107[94], Asymmetric arylation of the cyclic acetal 108 with phenyl triflate[95] using Pd-BINAP afforded 109, which was converted into the 3-phenyllactone 110 in 72% ee[96]. Addition of a molecular sieve (MS3A) shows a favorable effect on this arylation. The reaction of the 3-siloxycyclopentene 111 with an alkenyl iodide affords the. silyl... 

Figure 8-5. Proposed mechanism for the catalytic arylation of 2,3-dihydrofuran with phenyl triflate in the presence of Pd(OAc)2-(i )-BINAP catalyst.

The reactive zwitterions arising from the nucleophilic attack of imines 479 on the benzyne generated in situ from 2-(trimethylsilyl)phenyl triflate 478 proved to be an appropriate molecular scaffold for the capture of CO2 with sufficient electrophilicity to yield 2-aryl-3,l-benzoxazin+-ones 480 (Equation 53). Both substituents of the C=N bond affected the course of the reaction considerably the best yields were achieved by using imines with electron-rich or neutral aryl groups on the carbon, and benzyl or nonbranched chain alkyl substituents on the nitrogen atom. With substituted derivatives of 478, the unsymmetrically substituted arynes led to regioisomeric products <2006JA9308>. 

Cycloaddition of benzyne intermediates with aminothiazadienes provide access to substituted 2,4-diamino-4//-l,3-benzothiazines 196 in high yields. The benzynes are prepared by the treatment of (phenyl)[o-(trimethylsilyl)aryl]-iodonium triflates with 1.5 equiv of tetrabutylammonium fluoride (Scheme 20). Interestingly, 3-substituted-l,2-benzisothiazoles 197 are obtained when 4 equiv of tetrabutylammonium fluoride is used <2005H(65)1615>. 

There has been a summary of the use of insertion reactions of arynes into a-bonds to prepare nrt/io-disubs tituted arenes. A key to the success of these processes is the ability to generate benzyne under mild conditions by the reaction of readily available o-(trimethylsilyl)phenyl triflate with fluoride ions.61 Reaction of amines and their derivatives with benzynes generated in this way has been shown to be an efficient method for the production of N-arylated derivatives, as illustrated in Scheme 8. The method also works well in the O-arylation reactions of phenols and carboxylic acids 62... 

The self-condensation of iodosylbenzene was the first reported synthesis of a diaryliodonium salt back in 1892. The mechanism of the reaction was delineated only recently. This approach served for the synthesis of p-(phenylene)bis-(aryliodonium) salts [47], as well as some oligomers from (diacetoxyiodo)ben-zene and triflic acid [117], followed by coupling with an arene (Scheme 39). Under suitable conditions the same reaction can lead to simple phenyl(aryl)-iodonium triflates [118]. 

Perfluoroalkyl(phenyl)iodonium sulfonates 42 (also known as FITS reagents), as well as lFf,lff-perfluoroalkyl(aryl)iodonium triflates 44, have found practical application as electrophilic fluoro alkylating reagents toward a... 

Asymmetric Fleck reactions have been carried out with considerable success. The arylation of 2,3-dihydrofuran (38) with phenyl triflate using BINAP (XXXI) as a chiral ligand gave 2-phenyl-2,3-dihydrofuran (42) with 96% ee. Addition of FI—Pd—X to the primary product 40 gives the intermediate 41, and /f-elimination affords the dihydrofuran 42 with 96% ee in 71% yield as the major product in the presence of l,8-bis(dimethylamino)naphthalene (39) as a base. Another dihydrofuran 40 with 67% ee was obtained in 7%, showing that one enantiomer of 40 is converted to 42 with high selectivity [24]. 

Reaction of 2,3-dihydrofuran with aryl triflate in benzene in the presence of a base and a palladium catalyst, prepared in situ from Pd(OAc)2 and 2 equivalents of (R)-BINAP, gave (R)-2-aryl-2,3-dihydrofuran (2) and a small amount of the regioisomer (5)-2-aryl-2,3-dihydrofuran (3) (Scheme 1). Table I demonstrates that the arylation reaction proceeds in extremely high enantioselectivity with a variety of aryl triflates. Particularly, almost enantiomerically pure (R)-2 was obtained with 2-naphthyl triflate and phenyl triflates bearing an electron-withdrawing substituent at the para or meta position. 

Table II. Effect of Base on the Catalytic Asymmetric Arylation of 2,3-Dihydrofuran with Phenyl Triflate (la)a...

A model reaction is the asymmetric arylation of dihydrofuran 198 (Scheme 3-49) [205, 206]. Whereas coupling of 198 with iodoarenes gave only low enantiomeric excesses in the presence of the Cj-symmetrical ligand (7 )-2,2 -bis(diphenylphosphanyl)-l,l -binaphthalene [(/ )-BINAP, 207)], its coupling with phenyl triflate, however, afforded (i )-2-phenyl-2,3-dihydrofuran [(i )-199] in up to 71% yield with up to 93% enantiomeric excess. In the reaction with iodobenzene, the BINAP ligand apparently reversibly dissociates from the... 

It was also demonstrated that organosilylstannanes can be used as the trimethylsilyl anion source. In this case, the acid chlorides gave poor results and it was found that aryl iodides were suitable substrates. Reaction of buta-1,3-diene with Phi and BujSnSiMej gave the 1,4-carbosilylation product in 50% yield as an E/Z 84 16 mixture. The use of phenyl triflate as the aryl source did not give the desired 1,4-addition product but afforded the 2 1 telomerization product from two molecules of diene and one trimethylsilyl group, in good yield. 

The application of ligand 102 has successfully been extended to derivatiza-tions of nitrogen containing substrates. Arylation of the 2,3-dihydropyrrole 63 with phenyl triflate catalyzed by the 102-palladium complex [R=C(CH3)3] produced the single isomer 65 with 88% yield and in 85% ee [81]. 

Kappe and Stadler have developed an MW procedure for rapid production of triaryl phosphines by coupling diphenylphospine with aryl halides and triflates [134]. Taking into account the importance of phosphine ligands in a variety of transition metal-catalyzed reactions, convenient procedures for their production is valuable. Both homogeneous Pd-Ni and heterogeneous Pd catalysts were explored and the more unusual substrate phenyl triflate could also be coupled swiftly by use of nickel catalysis (Scheme 15.68). Couplings with other aryl halides proceeded in 26-85% yield after 3-30 min microwave irradiation at 180-200 °C. 

Various unsymmetrically substituted diaryliodonium triflates 269 can be synthesized by the reaction of iodosylbenzene [380] or (diacetoxyiodo)arenes [381] with arenes in trifluoromethanesulfonic acid (Scheme 2.76). This simple procedure affords diaryliodonium triflates in relatively high yields, but it is limited to aromatic substrates that are not sensitive to strong acids. In a milder, more selective variation of this procedure (diacetoxyiodo)benzene is reacted with arylboronic acids in the presence of triflic acid at -30 °C to afford aryl(phenyl)iodonium triflates in 74-97% yields [377]. 

A similar approach to aryl- and heteroaryl(phenyl)iodonium triflates 285 involves the ligand-transfer reaction between vinyliodonium salt 284 with aryllithiums (Scheme 2.83) [405]. Likewise, the reaction of ( )-[(3-(trifluoromethanesulfonyloxy)ethenyl](aryl)iodonium triflates 286 with aryllithiums or alkynyllithiums can be used for a selective preparation of the respective diaryl- or alkynyl(aryl)iodonium triflates in high yields [406]. 

Two further examples for arylation reactions catalyzed by phosphinooxazoline-palla-dium complexes are shown in Scheme 31 with the formation of 129 and 131 as nitrogen-containing substrates arylation of the 2,3-dihydropyrrole 63 with phenyl triflate catalyzed by the palladium complex 120 (R = CMcs) gave the single isomer 65 in 88% yield and with 85% ee.[ i... 

By employing o-(trimethylsilyl)phenyl triflate derivatives (11) as the aryne precursors, Larock and coworkers have developed a facile transition metal-free N-arylation method for amines, sulfonamides and carbamates under very mild reaction conditions (Scheme 12.4) [11]. Aromatic and aliphatic, as well as primary and secondary amines, react well, afTording good to excellent yields of the desired products. Secondary amines generally react faster than primary amines in... 

Remarkably, Beller s group developed several novel methodologies for the primary amides synthesis [135-139]. In the presence of palladium catalysts, aryl halides, phenyl triflates, benzyl chlorides and even phenols were transformed into the corresponding primary amides in good to excellent yields. Ammonia gas was used directly as an amine source and also as a base. These were the primary reports on using NH3 and CO for primary amides synthesis (Scheme 2.14). 

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