Enantioselective Rhodium-Catalyzed Addition of Arylboronic Acids to Alkenylheteroarenes

Pattison, Graham; Piraux, Guillaume; Lam, Hon Wai

doi:10.1021/ja106809p

Cited by 162 publications

(54 citation statements)

References 48 publications

(30 reference statements)

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“…Using 5 mol % of a complex of rhodium bound to the chiral diene L2, a 2-alkenylquinoxaline underwent alkenylation with (E)-2-phenylvinyl MIDA boronate (1.2 equiv) in 5:1 dioxane/H 2 O in the presence of K 3 PO 4 (2 equiv) at 60°C, though the yield and enantioselectivity of this reaction were modest (eq 8). 31 The use of an alkenyl MIDA boronate as a slow-release surrogate for the corresponding alkenylboronic acid was essential. Use of the alkenylboronic acid itself (2.4 equiv) under otherwise identical conditions led to only ~25% conversion, primarily because alkenylboronic acids undergo rapid protodeboronation under the aqueous, basic reaction conditions typically required for rhodium-catalyzed 1,4-additions.…”

Section: Scheme 7 Enantioselective Rh-catalyzed Arylation Of Alkenylmentioning

confidence: 99%

C═N-Containing Azaarenes as Activating Groups in Enantioselective Catalysis

2013

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Nitrogen-containing aromatic heterocycles (azaarenes) are of widespread chemical significance, and chiral compounds containing azaarenes feature prominently in pharmaceuticals, agrochemicals, and natural products. ThisPerspective highlights the use of a relatively underdeveloped strategy to prepare chiral azaarene-containing compounds: exploitation of the C=N bond embedded within certain azaarenes to activate adjacent functionality in catalytic asymmetric reactions. Work in this area has resulted in the development of several different types of catalytic enantioselective processes, including reductions, nucleophilic additions, and reductive couplings. It is hoped that this Perspective will encourage more researchers to work in this promising area.

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Section: Scheme 7 Enantioselective Rh-catalyzed Arylation Of Alkenylmentioning

confidence: 99%

C═N-Containing Azaarenes as Activating Groups in Enantioselective Catalysis

2013

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“…[13][14][15] The mostly poor conversions into the desired products may be explained by the fact that alkenylrhodium species are less stable than arylrhodium species, which renders protodeboronation or other decomposition pathways highly competitive with imine addition. [24] However, it is more difficult to rationalize the low enantioselectivities obtained when alkenylation was successful ( Table 1, entries 3, 4, 7, and 8). One factor to consider in all catalytic asymmetric additions to imines is the possibility of E/Z isomerization of the imine during the reaction, which usually has a negative impact upon stereoselectivity.…”

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confidence: 99%

Enantioselective Rhodium‐Catalyzed Addition of Potassium Alkenyltrifluoroborates to Cyclic Imines

2012

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Chiral a-branched allylic amines are important building blocks for organic synthesis, and several catalytic asymmetric methods have been developed for their synthesis. For example, the enantioselective metal-catalyzed amination of allylic electrophiles [1][2][3] and the rearrangement of allylic imidates [4][5][6] have proven to be highly effective. An alternative approach to chiral allylic amines that can be advantageous from the viewpoint of convergency is the catalytic enantioselective union of an alkenyl nucleophile with an imine. [7][8][9][10][11][12] In view of the widespread success of enantioselective Rh Icatalyzed additions of arylboron reagents to imines as a means to access chiral a-aryl-branched amines, [13][14][15] the development of the corresponding reactions of alkenylboron reagents to prepare chiral a-branched allylic amines should be an attractive goal. Surprisingly, however, only very limited precedent exists for this transformation. [16] Brak and Ellman have developed highly diastereoselective Rh I -catalyzed additions of alkenylboron reagents to N-tert-butanesulfinyl aldimines (Scheme 1 A). [17] The only existing enantioselective variant is that of Shintani, Hayashi, and co-workers, who, as part of a study involving additions of potassium aryltrifluoroborates to N-sulfonyl ketimines, also described one example using an alkenyltrifluoroborate (Scheme 1 B). [15c] Also of relevance is a single example of an enantioselective Rh Icatalyzed addition of an alkenylsilane to an N-sulfonyl aldimine. [18] Therefore, a general enantioselective Rh I -catalyzed addition of alkenylboron reagents to imines remains undeveloped.Herein, we demonstrate that cyclic imines are highly effective substrates for enantioselective Rh I -catalyzed additions of potassium alkenyltrifluoroborates, [19,20] providing products in excellent enantioselectivities and generally good yields. The cyclic structure of these imines, in which the C = N bond is constrained in the Z geometry, appears to be important for the success of the reactions.This study began with the attempted alkenylation of acyclic imines 1 a-d with potassium (E)-1-hexenyltrifluoroborate (2 equiv) at 80 8C in dioxane for 24 h in the presence of MeOH (5 equiv) and 1.5 mol % of the dimeric rhodium complexes derived from chiral diene ligands [21,22] L1 [15a] or L2 [23] (Table 1). Given that imines 1 a-d are highly effective Scheme 1. Rh I -catalyzed additions of alkenylborons to imines. MIDA = N-methyliminodiacetic acid.Table 1: Attempted Rh-catalyzed alkenylation of various imines. Entry Imine Ligand Product Yield [%] [a] ee [%] [b]

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“…[23] This report represents an improvement of the previous reaction conducted with a compound containing (2S)-(2,5-dimethylpyrrol-1-yl)-(1S)-cyclohexylamine as the amino group of the ligand. [24] The azaarene group spans from monocyclic oxazole, 1,2,4oxadiazole, 1,3,4-oxadiazole, pyrimidine, pyrazine, triazine, to bicyclic compound as quinoline, quinazoline, benzoxazole, and benzothiazole. The R group can be aliphatic, cycloaliphatic, benzyl or aryl.…”

Section: Unsaturated Alkyl Azaarenesmentioning

confidence: 99%

Enantioselective Synthesis of Alkyl Azaarenes

Meazza

Rios

2019

Asian J Org Chem

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This Minireview covers reports on the enantioselective synthesis of alkyl azaarenes since 2014. It deals with the latest achievements on the reactivity of alkyl azaarenes aiming at the preparation of more complex azaarenes containing chiral centers. They rely on the activating properties of the nitrogen atom when opportunely coordinated with a metal complex or Brønsted acid and possibly containing chiral ligands. In addition, conveniently located electron-withdrawing activating functional groups help increase the reactivity of the azaarenes. The same concepts operate in the case of vinyl azaarenes.[a] Dr. Scheme 1. Modes of activationScheme 2. Early example by Lam. 2 3 4 5 6 7 8

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Enantioselective Rhodium-Catalyzed Addition of Arylboronic Acids to Alkenylheteroarenes

Abstract: In the presence of a rhodium complex containing a newly developed chiral diene ligand, alkenes activated by a range of π-deficient or π-excessive heteroarenes engage in highly enantioselective conjugate additions with various arylboronic acids.

Cited by 162 publications

References 48 publications

C═N-Containing Azaarenes as Activating Groups in Enantioselective Catalysis

C═N-Containing Azaarenes as Activating Groups in Enantioselective Catalysis

Enantioselective Rhodium‐Catalyzed Addition of Potassium Alkenyltrifluoroborates to Cyclic Imines

Enantioselective Synthesis of Alkyl Azaarenes

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