Asymmetric Construction of Quaternary Carbon Stereocenter by Pd-Catalyzed Intramolecular .ALPHA.-Arylation

Arao, Takafumi; Kondo, Kazuhiro; Aoyama, Toyohiko

doi:10.1248/cpb.54.1743

Cited by 33 publications

(8 citation statements)

References 17 publications

(15 reference statements)

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“…8 The use of different amides in the presence of carbene ligands 1 or 2 and Pd 2 (dba) 3 as catalyst provided chiral oxindoles in good yields and enantioselectives (Scheme 3). A similar work in the palladium-catalyzed asymmetric intramolecular amide a-arylation using (S)-H 8 -BINAP was reported by Aoyama, 9 showing almost the same range of yields and enantioselectivities (Scheme 4).…”

Section: Figure 1 Examples Of Molecules Possessing Benzylic Quaternary Centerssupporting

confidence: 66%

Catalytic Enantioselective α-Arylation of Carbonyl Compounds

Burtoloso¹

2009

Synlett

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Enantioselective creation of benzylic quaternary centers still is a continuous challenge to many synthetic organic chemists. Among the existing methods for installation of this type of center, the direct asymmetric a-arylation of carbonyl compounds is very attractive due to the ready availability of the coupling substrates. Herein, we present some new tools to the catalytic asymmetric aarylation of carbonyl compounds that overcame many of the drawbacks posted in previous methods for this type of reaction.Benzylic quaternary centers are widely found in the structure of a considerable number of natural and pharmaceutically important compounds. Possessing either simple or complex molecular architectures ( Figure 1) these compounds still challenge many synthetic organic chemists, especially with respect to the enantioselective creation of those benzylic quaternary centers. 1 Figure 1 Examples of molecules possessing benzylic quaternary centersAmong the emerged methods for installation of this type of center, the direct asymmetric a-arylation of carbonyl compounds is very attractive due to the ready availability of the coupling substrates. Considering the versatility of the carbonyl group, asymmetric a-arylation of carbonyl compounds is not only limited to the creation of the benzylic center a to a carbonyl, but it can also be employed to generate benzylic centers with other functionalities. Two main methods can be outlined as direct and simple tools for the a-arylation of carbonyl compounds: (1) the nucleophilic aromatic substitution between enolates and aryl halides 2 and (2) transition-metal-catalyzed a-arylation of carbonyl compounds. 3 Although both methods can furnish a-arylated carbonyl compounds in a direct fashion, the former suffers many drawbacks such as the requirement of aromatic compounds with good electron-withdrawing substituents (F, NO 2 ). Based on this fact, the later method has become the one of choice for this type of transformation and many different protocols have been described to date. Nevertheless, much effort is still necessary to put this emerging method in a mature position, especially in the field of catalytic asymmetric a-arylation of carbonyl compounds. For example, high enantioselective a-arylation of carbonyl compounds has only been achieved in a very limited number of cases and with specific substrates. Another point is the limitation of those methods to provide only quaternary centers, which brings a challenge when epimerizable tertiary centers containing an aryl group are desirable. Herein, first, we would like to call the attention for this important and versatile emerging area giving an up-to-date overview of these main methods. Second, stimulate new contributions to this field. Third, to present very recent literature results as new tools to the catalytic asymmetric a-arylation of carbonyl compounds that overcame some of the drawbacks posted above.The first three general methods for the direct transitionmetal-catalyzed a-arylation of carbonyl compounds appeared independently in ...

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Section: Figure 1 Examples Of Molecules Possessing Benzylic Quaternary Centerssupporting

confidence: 66%

Catalytic Enantioselective α-Arylation of Carbonyl Compounds

Burtoloso¹

2009

Synlett

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“…Until this point, only modest enantioselectivities had been obtained in asymmetric cyclizations of 2-haloanilides to oxindoles, using catalytic systems composed of either Pd(0) or Pd(II) and several chiral NHC ligands (Figure 8 After an intensive screening of phosphane ligands, they found that acceptable levels of both the yield and the enantioselectivity of the enantioselective intramolecular α-arylation of an ortho-bromo amide could be achieved (98% yield and 68% ee) [81].…”

Section: Arylation Of Amidesmentioning

confidence: 99%

α‐Arylation Processes

2014

Catalytic Arylation Methods

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“…The capture of a Heck intermediate was beautifully employed by Overman and Rosen in a total synthesis of (-)-spirotryprostatin B (78,Scheme 20). [65] More specifically, treatment of the cyclisation precursor 76 with Pd 2 (dba) 3 and P(o-tol) 3 in the presence of KOAc gave a 1:1 mixture of the desired diastereoisomer 77a and the 3,18bis-epi-compound 77b.…”

Section: Oxindoles Through Tandem/domino Heck Reactionsmentioning

confidence: 99%

“…The stereoselective course of the reaction indicates an outer-sphere mechanism for the allylic substitution (antiattack). Finally, removal of the SEM protecting group gave (-)-spirotryprostatin B (78). The use of the 3,18-E-configured cyclisation precursor 76 was crucial, because the corresponding Z isomer resulted in a mixture of epimeric compounds at C(3) and C (18).…”

Section: Oxindoles Through Tandem/domino Heck Reactionsmentioning

confidence: 99%

“…An extensive phosphane ligand screening by Arao et al, for example, identified (S)-H 8 -BINAP (103c) as a superior phosphane ligand (Table 4, Entry iv). [78] Most success, however, came with the use of chiral oxazoline-derived NHC ligands. Glorius et al, for example, developed the ligand 103d, which provided the product in 43 % ee (Table 4, Entry v).…”

Section: Oxindoles Through Enolate Arylationsmentioning

confidence: 99%

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