Erythro-directive reduction of .alpha.-substituted alkanones by means of hydrosilanes in acidic media

Fujita, Makoto; Hiyama, Tetsuo

doi:10.1021/jo00258a004

Cited by 83 publications

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“…[12,13] Hydroxy ketones of type A and C have been synthesised among others by direct oxidation of enolates, although with low levels of stereoinduction, [14] by treatment of chiral hydroxy acids with a vinyllithium reagent, [15] by addition of 1-lithio-1-methoxyallene to a chiral ketone followed by hydrolysis, [16] by addition of an umpoled a,b-unsaturated acyl anion to aldehydes, [17] or by aldol reaction between aldehydes and protected hydroxy ketones in the presence of sodium hydride and butanol.…”

Section: Full Papersmentioning

confidence: 99%

α,β‐Unsaturated Aldehydes as Substrates for Asymmetric CC Bond Forming Reactions with Thiamin Diphosphate (ThDP)‐Dependent Enzymes

et al. 2008

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The enzymes benzaldehyde lyase (BAL) from Pseudomonas fluorescens, benzoylformate decarboxylase (BFD) from Pseudomonas putida and pyruvate decarboxylase (PDC) from Saccharomyces cerevisiae provide different C À C bond forming possibilities of a,b-unsaturated aldehydes with aliphatic and aromatic aldehydes. Structure elucidation and determination of the absolute configuration of the products, which were obtained with high regio-and stereoselectivity were carried out. Selective 1,2-reactivity with yields of 75% and > 98% ee, for one single isomer (A) were obtained, by choosing the suitable enzyme in combination with the appropriate substrates. By varying enzymes or substrates the regioisomeric hydroxy ketones C, with up to > 99% ee, can be obtained. The application of these new chiral building blocks in the synthesis of natural products or biological active substances is considerably facilitated by applying the different ThDP-dependent enzymes as catalysts.Abbreviations: BAL, benzaldehyde lyase; BFD, benzoylformate decarboxylase; PDC, pyruvate decarboxylase; His, hexahistidine; 2-HPP, 2-hydroxy-1-phenylpropan-1-one; PAC, phenylacetylcarbinol; NTA, nitrilotriacetic acid; ThDP, thiamin diphosphate; wt, wild-type.Keywords: benzaldehyde lyase; benzoylformate decarboxylase; biocatalysts; pyruvate decarboxylase; stereochemistry IntroductionThiamin diphosphate (ThDP)-dependent enzymes are well-known to catalyse a broad range of asymmetric reactions.[1] Enzymes of this class like benzaldehyde lyase (BAL) from Pseudomonas fluorescens, [2] benzoylformate decarboxylase (BFD) from Pseudomonas putida [3] and pyruvate decarboxylase (PDC) from Saccharomyces cerevisiae [4] enable various modes of C À C bond forming reactions. Besides the physiological reactivity, several of these enzymes can catalyse, for example, the C À C bond formation between two aldehydes, giving chiral 2-hydroxy ketones with high enantioselectivity. The reactions of aromatic aldehydes as donor and aliphatic aldehydes as acceptor give rise to 2-hydroxy-1-phenyl-1-propanone derivatives with S absolute configuration in the case of BFD catalysis [5] and R for BAL.[6] If aromatic aldehydes are employed as donor and acceptor, (R)-benzoins are optained with both enzymes. [7,8] (R)-Phenylacetylcarbinol is formed in the PDC-catalysed reaction of decarboxylated pyruvate with benzaldehyde as acceptor aldehyde. [4,9] Here we describe the use of a,b-unsaturated aldehydes as substrates for C À C bond ligation in BAL-, BFD-and PDC-catalysed reactions. These substrates might act as donor and as acceptor for the 1,2-(A, C) and the 1,4-addition (B, D) (Scheme 1). Adv. Synth. Catal. 2008, 350, 759 -771 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 759 FULL PAPERSIn reactions according to Equation (1) the a,b-unsaturated aldehyde is bound to ThDP and reacts as donor resulting in the formation of hydroxy ketone A or hydroxy enone B. In reactions according to Equation (2) the a,b-unsaturated aldehyde is attacked by an "active aldehyde" and reacts as acceptor resulti...

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Section: Full Papersmentioning

confidence: 99%

α,β‐Unsaturated Aldehydes as Substrates for Asymmetric CC Bond Forming Reactions with Thiamin Diphosphate (ThDP)‐Dependent Enzymes

et al. 2008

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“…[5] On the other hand, hydrosilanes [6] have become viable reducing agents, which are used in industry on the ton scale for various processes. Notably, they tolerate air and moisture but promote the reduction of aldehydes and ketones along with alkenes and alkynes in the presence of Brønsted [7] and Lewis acids [8] and bases, [9] as well as transition metals. [10][11][12][13] In the last decade, significant progress has also been achieved for hydrosilylations of carboxamides in the presence of noble-metal-based catalysts.…”

Section: Introductionmentioning

confidence: 99%

Zinc‐Catalyzed Chemoselective Reduction of Tertiary and Secondary Amides to Amines

Das

Addis

Junge

et al. 2011

Chemistry A European J

149

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General and convenient procedures for the catalytic hydrosilylation of secondary and tertiary amides under mild conditions have been developed. In the presence of inexpensive zinc catalysts, tertiary amides are easily reduced by applying monosilanes. Key to success for the reduction of the secondary amides is the use of zinc triflate and disilanes with dual Si-H moieties. The presented hydrosilylations proceed with excellent chemoselectivity in the presence of sensitive ester, nitro, azo, nitrile, olefins, and other functional groups, thus making the method attractive for organic synthesis.

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“…Substrates 11b-g bearing an electronwithdrawing group at the para-position of the phenyl ring (i.e., halogen, ester, nitrile, nitro or trifluoromethyl group) gave the corresponding α-alkoxyketones 12b-g in 69-89% yields ( Table 2, entries 1-6). In contrast, substrates bearing an electron-donating group at the para position, such as a methyl or methoxy group, gave much lower yields of the corresponding α-alkoxyketone products, with the para-methoxy substrate providing only a trace amount of the product (Table 2, entries 7,8). Substrates bearing a methoxy or nitro group at the meta-position reacted smoothly to afford the desired products 12j and 12k, with the electron-withdrawing group providing a better yield (84%) than the electron-donating group (58%) ( Table 2, entries 9, 10).…”

Section: Resultsmentioning

confidence: 99%

“…1). α-Acyloxyketone has also been used as a simple starting material for the stereoselective synthesis of a variety of different structures, including numerous 1,2-diols [4][5][6][7][8] and heterocyclic systems. [9][10][11] Based on the importance of α-acyloxyketones to chemistry, the development of a concise synthetic method for the preparation of α-acyloxyketone derivatives is important.…”

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Synthesis of α-Acyloxyketone Derivatives <i>via</i> the Platinum-Catalyzed Migration of Propargylic Esters

Tsukano

Yamamoto

Takemoto

2015

CHEMICAL & PHARMACEUTICAL BULLETIN

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The synthesis of α-acyloxyketones via the migration of a propargylic ester followed by the intramolecular nucleophilic addition of the resulting allene was achieved using a cationic platinum catalyst. The optimized conditions for this transformation were determined to be 3 mol% of Pt(cod)Cl 2 , 3 mol% of AgNTf 2 , and 3 eq of water in toluene at 100°C, and these conditions were successfully applied to the synthesis of a wide variety of α-aryl-α-acyloxyketones. The mechanism of this reaction was evaluated in detail based on the results of isotope labeling experiments using H 2 18 O.Key words platinum; propargylic ester migration; α-acyloxyketone α-Acyloxyketone, which is a protected form of α-hydroxyketone, is a fundamental structure that can be found in a broad range of natural products and bioactive compounds, including hainanmurpanin, 1) paniculatin 2) and murpaniculol senecioate 3) (Fig. 1). α-Acyloxyketone has also been used as a simple starting material for the stereoselective synthesis of a variety of different structures, including numerous 1,2-diols 4-8) and heterocyclic systems.9-11) Based on the importance of α-acyloxyketones to chemistry, the development of a concise synthetic method for the preparation of α-acyloxyketone derivatives is important. Although a wide variety of synthetic methods have been investigated to date, 12,13) reports pertaining to the direct synthesis of α-acyloxyketone III by the oxidation of alkyne I are rare, most likely because of the difficulties associated with suppressing the over-oxidation of the product and controlling the regioselectivity of the reaction 14-16) (Chart 1). To allow for the direct synthesis of α-acyloxyketone III from alkyne I, several researchers directed their attention towards the transition metal-catalyzed migration of propargylic esters [17][18][19][20] to affect a facile oxidative transformation. [21][22][23][24][25][26][27][28][29][30] For example, in 1991, Schick and Mahrwald 21) reported that the treatment of propargyl acetate 1 with PdCl 2 (MeCN) 2 gave a 1 : 1 mixture of α-acyloxyketone 2 and α,β-unsaturated ketone 3 via the rearrangement of the acetyl group (Chart 2(a)). Ohfune et al. 24)also reported the synthesis of α-acyloxy-α′-siloxyketone 4 using a gold catalyst (Chart 2(b)). Under Ohfune's conditions, it was observed that substrates without a silyl group did not undergo the reaction, and it was therefore assumed that the silyl group was essential for stabilizing the β cation of reaction intermediate 5 (or 6). Although these reactions provided facile access to the α-acyloxyketones 2 and 4 from the readily accessible propargyl esters 1 and 3, several opportunities still remained to improve on this reaction in terms of the selectivity and substrate scope. For improving the scope of this reaction, we focused on enhancing the π-acidity of the transition metal catalyst (i.e., palladium, gold or platinum catalyst) by decreasing its electron density. [17][18][19][20] If allene 9, which was derived from 7, could be strongly activated by a π-a...

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Erythro-directive reduction of .alpha.-substituted alkanones by means of hydrosilanes in acidic media

Cited by 83 publications

References 0 publications

α,β‐Unsaturated Aldehydes as Substrates for Asymmetric CC Bond Forming Reactions with Thiamin Diphosphate (ThDP)‐Dependent Enzymes

α,β‐Unsaturated Aldehydes as Substrates for Asymmetric CC Bond Forming Reactions with Thiamin Diphosphate (ThDP)‐Dependent Enzymes

Zinc‐Catalyzed Chemoselective Reduction of Tertiary and Secondary Amides to Amines

Synthesis of α-Acyloxyketone Derivatives <i>via</i> the Platinum-Catalyzed Migration of Propargylic Esters

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