BINAP ligand triflates

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... 

Chiral //A(oxazolinc) ligands disubstituted at the carbon atom linking the two oxazolines by Frechet-type polyether dendrimers coordinated with copper(II) triflate were found to provide good yields and moderate enantioselectivities for Mukaiyama aldol reactions in water that are comparable with those resulting from the corresponding smaller catalysts.291 AgPF6-BINAP is very active in this reaction and the addition of a small amount of water enhanced the reactivity.292... 

A palladium-catalyzed protocol for carbon-sulfur bond formation between an aryl triflate and para-methoxybenzylthiol was introduced by Macmillan and Anderson (Scheme 6.66) [138], Using palladium(II) acetate as a palladium source and 2,2 -bis(diphenylphosphino)-l,l -binaphthyl (BINAP) as a ligand, microwave heating of the two starting materials in N,N-dimethylformamide at 150 °C for 20 min in the presence of triethylamine base led to the formation of the desired sulfide in 85% yield. 

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>. 

The reaction is carried out with aryl triflates and other details such as solvent and base used are also important. Intramolecular additions of aryl halides or triflates to alkenes in a side-chain leading to cyclic compounds have been reported by Overman [24], Rather complicated ring structures can be made stereospecifically. While initially BINAP seemed the best ligand for this conversion, the number of useful ligands is increasing [25],... 

With (i ,i )-BINAP as the ligand, Keay and Lau have been able to achieve the cascade cyclizations of the dienyl-substituted aryl triflates 134 toward the total synthesis of the natural product (+)-halenaquinone with ee s of up to 96% (Scheme 35). For these substrates, they observed an interesting influence of the remote substituent in 134. ... 

Enantioselective carbonylative cyclization has been realized with o-alkenylaryl triflates in the presence of 2,2-bis(diphenyl-phosphanyl)-1,1-binaphthyl (BINAP) or TolBINAP ligands in high material yields and enantiomeric excess (Equation (41)). ... 

In an oxidative addition, Pd(0) complex 22 with BINAP as a ligand accepts alkenyl triflate It. The resulting Pd complex 23 is cationic, since the triflate anion is bound only loosely to the palladium and dissociates from the complex.1 Syn insertion of one of the two enantiotopic double bonds of the cyclopentadienc into the alkenyl-Pd bond of complex 23 leads firs to q -allyl-Pd complex 24. This is in rapid equilibrium with t 3-allyl-Pd complex 25. Neither 24 nor 25 contains a p-H atom in a yn relationship to palladium. Moreover, internal rotation is impossible in the con form a-tionaily fixed ring system. For this reason there is no possibility of a subsequent p-hydride elimination that would once again release the palladium catalyst. In a normal Heck reaction (see discussion) the catalytic cycle would be broken at this point. 

Extensive studies by Amatore, Jutand, and co-workers have shed light on the structure and oxidative addition chemistry of a number of synthetically important palladium complexes [42], In particular, these workers have shown that the major species in a solution of Pd(dba)2 and BINAP is Pd(dba)BINAP and that oxidative addition of Phi to this complex generates (Bl-NAP)Pd(Ph)I [42d,43], In addition, it has been demonstrated that palladium halide complexes such as (PhjP jaryljPdCl do not dissociate the halide ligand in DMF solution [44], whereas the corresponding triflate complex is completely dissociated [44,45], As noted earlier, the nature of the oxidative addition intermediates defines two mechanistic pathways for the Heck reaction the neutral pathway for unsaturated halide substrates and the cationic pathway for unsaturated triflate substrates [2c-g,3,7-9]. Further, it is possible for halide substrates to be diverted to the cationic pathway by addition of Ag(I) orTh(I) salts [3], and it is possible to divert some triflate substrates to the neutral pathway by addition of halide additives [38]. Individual steps of these two pathways have recently received some scrutiny. 

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]. 

Asymmetric cyclization using chiral ligands offers powerful synthetic methods for the preparation of optically active compounds [39]. After early attempts [40,41], satisfactory optical yields have been obtained in a number of cases. Synthesis of the optically active cA-decalin system [42] was carried out with high enantioselectivity based on the differentiation of enantiotopic C=C double bonds [43]. The cyclization of the triflate 93 gave the cA-decalin 94 with 95% ee in 78% yield using (i )-BINAP. A mixture of 1,2-dichloroethane and f-BuOH is the best solvent, and the asymmetric synthesis of vemolepin (96) via Danishefsky s key intermediate 95 has been achieved [44]. 

Palladium(O) complexes containing P(o-C6H4Me)3 as ligand show low reactivity toward aryl triflates [95,96]. Thus, the original catalyst is not effective for the ami-nation of aryl triflates. However, palladium complexes with the chelating phosphines DPPF and BINAP are effective [97,98]. Selected animations of aryl triflates by aniline are shown in Eq. (9), and selected animations of aryl triflates by alkylamines in Eq. (10). 

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