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... 

Larhed et al. investigated enantioselective Heck reactions with 2,3-dihydrofuran as alkene [86]. In the coupling with phenyl triflate, conditions previously reported by Pfaltz [87] were attempted under microwave irradiation. Interestingly, the catalytic system Pd2(dba)3/(4S)-4-t-butyl-2-[2-(diphenylphosphanyl)phenyl]-4,5-dihydro-l,3-oxazole, identified by the Swiss team, was found suitable for high-temperature microwave-assisted enantioselective Heck reactions (Scheme 76). Using a proton sponge as a base and benzene as a solvent gave the best conversions (Scheme 76). At tempera-... 

Equation 11.27 Stille coupling in solution with 4-acetyl phenyl triflate. 

A short five-step synthesis of a bifuran, namely ( )-2,2 -bis(diphenylphosphino)-3,3 -binaphtho[2,l-I>]furan (BINAPFu) from naphthofuranone via a low-valent titanium-mediated dimerization was reported. The newly developed resolution procedure for phosphines was utilized to provide the optically active bidentate phosphine ligands (BINAPFu), which consistently outperforms BINAP in the asymmetric Heck reaction between 2,3-dihydrofuran and phenyl triflate . Another way in which a benzofuranone can be converted into benzo[7 ]furan is by treatment of the former with 1-BU2AIH at -78°C followed by an acidic work up <00TL5803>. 

Benzyne, which is generated in situ from 2-(trimethylsilyl)phenyl triflate and KF, acts as an alkyne congener in distannation in the presence of palladium-/ r/-alkyl isocyanide complex.157 A variety of substituted benzyne derivatives inserts into the Sn-Sn bond to give l,2-bis(stannyl)benzenes (Equation (59)). The reaction fails to occur in the presence of other palladium catalysts such as Pd(PPh3)4. 

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 proposed mechanism is illustrated in Figure 8-5.60a Oxidative addition of the phenyl triflate to the palladium(0)-BINAP species A gives phenylpalla-dium triflate B. Cleavage of the triflate and coordination of 2,3-dihydrofuran on B yields cationic phenyl palladium olefin species C. This species C bears a 16-electron square-planar structure that is ready for the subsequent enantio-selective olefin insertion to complete the catalytic cycle (via D, E, F, and G). The base and catalyst precursor have profound effects on the regioselectivity and enantioselectivity. 

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>. 

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... 

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...

With chiral ligands the Heck reaction can be enantioselective. The amino-acid-derived phosphin ligand in the margin controls the Heck reaction of phenyl triflate with dihydrofnran. The ligan. selects one enantio topic face of the alkene (see Chapter 45 if you have forgotten this term) and th usual douhle hond migration and (3 elimination complete the reaction. 

A typical procedure for Eq. (64) [121] is as follows. A mixture of benzanilide (1 mmol), phenyl triflate (4 mmol), Pd(OAc)2 (0.05 mmol), PPhj (0.3 mmol), CS2CO3 (4 mmol), and toluene (8 ml) is stirred under nitrogen (with a balloon) at 110 °C for 24 h. After cooling, the reaction mixture is poured into dilute HCl, extracted with ethyl acetate, and dried over sodium sulfate. Evaporation of the solvent followed by washing the residual solid well with hexane gives the product. 

Table 1-12. Effects of ligand (L) and substrate ratios on the coupling between phenyl triflate and ( )-l-methoxy-l-(trimethylsiloxy)propene (L = phosphine ligand) (data from [165])...

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. 

To a solution of Pd(dba)2 (163 mg, 0.3 mmol, 5mol%) in THF (4mL) was added dppf (125 mg, 0.3 mmol, 5 mol%) at 0°C. After a few minutes, phenyl triflate (0.91 g, 4 mmol) was added, followed by a solution of 4-chlorophenylzinc bromide (6 mmol) in THF/hexane prepared as described for 4-cyanophenylzinc bromide above. The reaction mixture was heated to 60 °C for 1.5 h then, after cooling to rt, it was worked up as usual and the crude residue obtained after evaporation of the solvents was purified by flash chromatography (hexanes), affording the biphenyl 58 as a clear oil (695 mg, 92% yield). 

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