Reversal of Enantioselectivity in the Asymmetric Rhodium- versus Iridium-Catalyzed Hydroboration of Meso Substrates

Luna, Alejandro Pérez; Bonin, Martine; Micouin, Laurent; Husson, Henri‐Philippe

doi:10.1021/ja026714m

Cited by 83 publications

(29 citation statements)

References 17 publications

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“…[a] completely reversed, [27] led us to wonder whether the Ir-Binap system could also be a suitable catalyst for the hydroboration of vinylarenes. Thus, when the complex [Ir(cod)(R)-Binap]-BF 4 was used under the same hydroboration reaction conditions as the rhodium system, conversion was complete but enantioselectivity was almost zero and regioselectivity only about 30 % on 1-phenylethanol (Table 4.…”

Section: Resultsmentioning

confidence: 99%

“…Once again, the question of whether the insertion step or the coordination step in the catalytic cycle are the enantiodifferentiation key steps, is the starting point of discussion. Recently experimental [27] and theoretical studies [29] have proposed two main catalytic cycles that show that the enantiodifferentiation step in the iridium catalysed hydroboration involves the Ir-B migratory insertion step, while the rhodium catalysed hydroboration involves the Rh-H migratory insertion. However, we have calculated a considerable difference in the stability of the isomers when the substrate coordinates to the iridum(i) or rhodium(i) complexes.…”

Section: Resultsmentioning

confidence: 99%

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In Quest of Factors That Control the Enantioselective Catalytic Markovnikov Hydroboration/Oxidation of Vinylarenes

Segarra

Daura-Oller

Claver

et al. 2004

Chemistry A European J

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This study attempts to rationalise the unpredictable performance of transition metal catalysed asymmetric hydroboration of vinylarenes on varying the precursor of the catalyst from cationic to neutral species, [M(cod)(L-L)]BF4, [M(mu-Cl)(cod)]2/(L-L), the metal (M=Rh and Ir), and the hydroborating reagent (catecholborane, pinacolborane). The approaches are based on the agreement between experimental data provided by (R)-Binap and (R)-Quinap modified catalytic systems and computational data evidenced by DFT calculations and QM/MM strategies. Unprecedentedly high enantiomeric excesses in the hydroboration/oxidation of vinylarenes with both electron-withdrawing substituents ((R)-(+)-1-p-F-phenylethanol, ee up to 92 %) and electron-releasing substituents ((R)-(+)-1-p-MeO-phenylethanol, ee up to 98 %), can be attributed to a rhodium halide key intermediate.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

In Quest of Factors That Control the Enantioselective Catalytic Markovnikov Hydroboration/Oxidation of Vinylarenes

Segarra

Daura-Oller

Claver

et al. 2004

Chemistry A European J

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“…2.10 a) [42]. Interestingly, iridium catalysts give the opposite enantiomer in the hydroboration step, albeit with lower efficiency [43]. Although they are readily synthesized, cyclopropenes are infrequently used in asymmetric catalysis.…”

Section: Diphosphine Ligandsmentioning

confidence: 99%

Rhodium‐Catalyzed Hydroborations and Related Reactions

Brown¹

2005

Modern Rhodium‐Catalyzed Organic Reactions

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The development of metal-catalyzed hydroboration was initiated in a single paper by Männig and Nöth in 1985 [1]. They demonstrated that catecholborane reacted with simple alkenes in the presence of transition-metal catalysts, the most effective being Wilkinson's catalyst, RhCl(PPh 3 ) 3 . Since this reaction of catecholborane with alkenes is normally rather slow, even at elevated temperatures, this observation provided a real opportunity for catalysis. Prior to this work, the only precedent had been the addition of a secondary alkoxyborane to the same rhodium complex, giving a borylrhodium hydride analogous to known silylrhodium hydrides [2]. The synthetic potential of catalytic hydroboration was quickly realized and further extended through Burgess's demonstration of asymmetric catalysis [3], which was later refined and extended by Hayashi [4]. All this early work has been reported in a 1991 review [5], with a later and more extensive review by Belet'skaya and Pelter in 1997 [6]. As these reviews are readily available, the present chapter is confined largely to developments that have taken place since the beginning of 1997. Fig. 2.1 summarizes some of these early milestones. Although metal catalysts other than rhodium have been examined, for example in the palladiumcatalyzed hydroboration of allenes [7], the majority of the interesting developments have been made with rhodium.In the interim period, results have accumulated steadily, in endeavors to address and extend the chemistry beyond the initial perceived limitations. These limitations include the following: (a) the effective catalytic syntheses are confined to the reactions utilizing catecholborane; (b) the scope of alkenes for which efficient rate, regio-and enantioselectivity can be achieved is limited, and (c) the "standard" transformation mandates the oxidation of the initially formed (secondary) boronate ester to a secondary alcohol, albeit with complete retention of configuration [8]. Nonetheless, for noncatalytic hydroboration reactions that lead to the formation of a trialkylborane, a wide range of stereospecific transformations may be carried out directly from the initial product, and thereby facilitate direct C-N and C-C bond formation [9].A reaction pathway for catalytic hydroboration was suggested by Evans and co-workers [10], and amplified through computational studies [11]. This involves the rhodium acting through oxidative addition across the B-H bond, and the resulting borylrhodium hydride complexing to the alkene (reversibly). This is followed by a hydride migration, with a subsequent reductive elimination of the alkylboronate ester to complete 33 2

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“…Conversely, norbornene and its related derivatives have been hydroformylated selectively into the exo-formyl products in the presence of platinum and rhodium catalysts modified by chiral diphosphorous auxiliaries. [5,6] We have an ongoing interest both in asymmetric transformations involving bicyclic hydrazines to synthesize polyfunctional aminocyclopentanes [7][8][9] and hydroformylation. [10] As such, we reported recently on the rearrangement, [11,12] hydroboration [8,13,14] and asymmetric nucleophilic ring opening [15,16] of bicyclohydrazine derivatives.…”

Section: Introductionmentioning

confidence: 99%

Desymmetrization of meso‐Bicyclic Hydrazines by Rhodium‐Catalyzed Enantioselective Hydroformylation

Bournaud¹,

Lecourt²,

Micouin³

et al. 2008

Eur J Org Chem

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Reversal of Enantioselectivity in the Asymmetric Rhodium- versus Iridium-Catalyzed Hydroboration of Meso Substrates

Abstract: The Ir-catalyzed asymmetric hydroboration of bicyclic hydrazines with ee and chemical yields up to 64% is reported. The switch from rhodium to iridium leads systematically to opposite enantiomers in this desymmetrization reaction.

Cited by 83 publications

References 17 publications

In Quest of Factors That Control the Enantioselective Catalytic Markovnikov Hydroboration/Oxidation of Vinylarenes

In Quest of Factors That Control the Enantioselective Catalytic Markovnikov Hydroboration/Oxidation of Vinylarenes

Rhodium‐Catalyzed Hydroborations and Related Reactions

Desymmetrization of meso‐Bicyclic Hydrazines by Rhodium‐Catalyzed Enantioselective Hydroformylation

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