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BINAP Heck reaction

Asymmetric cyclization using chiral ligands has been studied. After early attempts[142-144], satisfactory optical yields have been obtained. The hexahy-dropyrrolo[2,3-6]indole 176 has been constructed by the intramolecular Heck reaction and hydroaryiation[145]. The asymmetric cyclization of the enamide 174 using (S j-BINAP affords predominantly (98 2) the ( )-enoxysilane stereoisomer of the oxindole product, hydrolysis of which provides the ( l-oxindole aldehyde 175 in 84% yield and 95% ec. and total synthesis of (-)-physostig-mine (176) has been achieved[146]. [Pg.154]

For the performance of an enantioselective synthesis, it is of advantage when an asymmetric catalyst can be employed instead of a chiral reagent or auxiliary in stoichiometric amounts. The valuable enantiomerically pure substance is then required in small amounts only. For the Fleck reaction, catalytically active asymmetric substances have been developed. An illustrative example is the synthesis of the tricyclic compound 17, which represents a versatile synthetic intermediate for the synthesis of diterpenes. Instead of an aryl halide, a trifluoromethanesul-fonic acid arylester (ArOTf) 16 is used as the starting material. With the use of the / -enantiomer of 2,2 -Z7w-(diphenylphosphino)-l,F-binaphthyl ((R)-BINAP) as catalyst, the Heck reaction becomes regio- and face-selective. The reaction occurs preferentially at the trisubstituted double bond b, leading to the tricyclic product 17 with 95% ee. °... [Pg.157]

The Shibasaki group [27] developed an enantioselective total synthesis of (+)-xes-toquinone (6/1-38) using an asymmetric double Heck reaction with BINAP as chi-... [Pg.362]

Shibasaki and coworkers [87] described the first enantioselective combination of this type in their synthesis of halenaquinone (6/1-162) (Scheme 6/1.43). The key step is an intermolecular Suzuki reaction of 6/1-159 and 6/1-160, followed by an enantioselective Heck reaction in the presence of (S)-BINAP to give 6/1-161. The ee-value was good, but the yield was low. [Pg.386]

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>. [Pg.157]

In these Heck reactions some degree of enantioselectivity (up to 83% ee) is achieved in the presence of (/ )-BINAP, although the yields of Heck products are often very low in the highest degree of enantioselectivity (e.g., 19% isolated yield at 83% ee) [93]. An example of a tandem Heck reaction is shown below involving the arylation of dihydropyrrole 132 with 1-naphthyl triflate (133) [92]. Complete chirality transfer is observed for the arylation of 134 to 135. [Pg.55]

Scheme 16. Results from the enantioselective Heck reaction using BINAP and PHOX. Scheme 16. Results from the enantioselective Heck reaction using BINAP and PHOX.
A fluorous version of the chiral bis-phosphine BINAP has been developed for asymmetric Heck reactions [5], Several fluorous-derivatized binaphthols and BINAP derivatives have been reported, (Scheme 10.4) [6], The silane spacer group present in one of the ligands was used to maximize the percentage fluorine on the molecule. Even so, the partition coefficient1 between FC-72 (see Chapter 3) and benzene was only 2.85, and not surprisingly, the reuse of the catalyst was poor. [Pg.197]

The use of cyclic alkenes as substrates or the preparation of cyclic structures in the Heck reaction allows an asymmetric variation of the Heck reaction. An example of an intermolecular process is the addition of arenes to 1,2-dihydro furan using BINAP as the ligand, reported by Hayashi [23], Since the addition of palladium-aryl occurs in a syn fashion to a cyclic compound, the 13-hydride elimination cannot take place at the carbon that carries the phenyl group just added (carbon 1), and therefore it takes place at the carbon atom at the other side of palladium (carbon 3). The normal Heck products would not be chiral because an alkene is formed at the position where the aryl group is added. A side-reaction that occurs is the isomerisation of the alkene. Figure 13.20 illustrates this, omitting catalyst details and isomerisation products. [Pg.285]

Desymmetxization by oxidative addition has been examined in a number of contexts. Erase reported that bisenolnonaflates undergo a desymmetrization/Heck reaction cascade with modest efficiency. " The use of BINAP as a ligand for Pd affords low ee s and poor yields ... [Pg.305]

Benzamido-cinnamic acid, 20, 38, 353 Benzofuran polymerization, 181 Benzoin condensation, 326 Benzomorphans, 37 Benzycinchoninium bromide, 334 Benzycinchoninium chloride, 334, 338 Bifiinctional catalysts, 328 Bifiinctional ketones, enantioselectivity, 66 BINAP allylation, 194 allylic alcohols, 46 axial chirality, 18 complex catalysts, 47 cyclic substrates, 115, 117 double hydrogenation, 72 Heck reaction, 191 hydrogen incorporation, 51 hydrogen shift, 100 hydrogenation, 18, 28, 57, 309 hydrosilylation, 126 inclusion complexes, oxides, 97 ligands, 19, 105 molecular structure, 50, 115 mono- and bis-complexes, 106 NMR spectra, 105 olefin isomerization, 96... [Pg.192]

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. [Pg.47]

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. [Pg.692]

Use of the allylsilanes as the alkene components in the Heck reaction is illustrated in the regioselective intramolecular cyclization of 120 (equation 98)180. In addition, a high enantioselectivity of 90 %ee is obtained when the chiral phosphine (S)-BINAP is employed. The propargylsilane analog undergoes a similar reaction181. [Pg.1827]

A similar procedure was employed in the asymmetric Heck-type coupling of iodonium salt 81 with 2,3-dihydrofuran (Scheme 38) [65]. When carried out in the presence of the chiral bidentate ligand (R)-BINAP, this reaction afforded optically active (up to 78% ee) coupling product 82 in moderate yield. [Pg.114]

The differentiation of enantiotopic C=C double bonds in the intramolecular Heck reaction of 1,3-diene 116 using (S)-BINAP, and subsequent regioselective carbanion capture of the 7i-allylpalladium intermediate 117 gave 118 with 87% ee with complete diastereo- and regioselectivity. A, ll2)-Capncllene (119) was synthesized from 118... [Pg.44]

The Shibasaki cychzation of mc.vo-cyclohexa-1,4-dienes in the presence of a chiral palladium complex and silver carbonate in l-methyl-2-pyrrolidinone is probably the first example of an enantioselective Heck reaction (Scheme 10.34).60 The enantiomeric excess could be slightly improved by replacing the chiral phosphine ligand BINAP with the corresponding less coordinating arsine ligand, as well as replacing silver carbonate with silver phosphate.61,62... [Pg.301]

The palladium-catalyzed arylation and alkenylation of olefins, which were first discovered in the 1970 s by Heck (7,2) and Mizoroki (3) and have been often called the "Heck reaction", are versatile synthetic means for making a carbon-carbon bond. These reactions have been extensively used for organic synthesis during the past two decades (4-7). However, no reports on the "asymmetric Heck reaction" have been appeared until very recently. Shibasaki reported an asymmetric intramolecular cyclization of alkenyl iodides to give c/j-decalin derivatives of 80-91% ee (8-10). Overman reported an intramolecular cyclization of alkenyl triflate, giving a chiral quaternary carbon center of 45% ee (77). We report herein the first example of intermolecular asymmetric Heck-type arylation of cyclic olefins catalyzed by (7 )-BINAP-coordinated palladium complexes (Scheme 1) (12,13). [Pg.80]

The famous ligand BINAP controls an intramolecular Heck reaction to give decalin derivative... [Pg.1324]

By converting the enol triflate 41 to the spiro-tricyclic dienone 42, Overman and co-workers had already shown in 1989 that the direct enantio-selective formation of quaternary chiral carbon centers ean be carried out through an intramolecular Heck reaction. While the enantioselectiv-ities were only moderate at the beginning [ 16], the same authors later succeeded in achieving the Pd(0)-BINAP-catalyzed cyclizalion of substrates of type 43 to spiro-oxindoles 44 with up to 95 % ee (Scheme 12) [17]. [Pg.139]


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See also in sourсe #XX -- [ Pg.191 ]




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