An Unusual Type of Ruthenium-Catalyzed Transfer Hydrogenation of Ketones with Alcohols Accompanied by C−C Coupling

Cho, Chan Sik; Kim, Bok Tae; Kim, Tae‐Jeong; Shim, Sang Chul

doi:10.1021/jo0108459

Cited by 202 publications

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“…4 Thus, when equimolar amounts of both substrates ([B]/[A] = 1) were used under similar ruthenium catalyst system, α-alkylated ketones D were preferentially formed (Scheme 1, route b). [5][6][7] In addition, we recently disclosed an unprecedented ruthenium-catalyzed coupling between secondary alcohols E and primary alcohols B which leads to secondary alcohols C (Scheme 1, route c).…”

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An Efficient Direct Synthesis of β-Ferrocenylketones Catalyzed by Ruthenium

2004

Bulletin of the Korean Chemical Society

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Transition metal-catalyzed carbon-carbon bond forming reaction has been widely used as a fundamental synthetic tool in organic synthesis.1 During the course of our ongoing studies on ruthenium-catalyzed organic syntheses and transformations, we recently found an unusual type of ruthenium-catalyzed transfer hydrogenation 2,3 of ketones by primary alcohols accompanied by C-C coupling.4,5 The preferential formation of coupled secondary alcohols C to coupled ketones D was attributed to the use of an excess amount of alcohols B to ketones A ([B]/[A] = 3) (Scheme 1, route a). 4 Thus, when equimolar amounts of both substrates ([B]/[A] = 1) were used under similar ruthenium catalyst system, α-alkylated ketones D were preferentially formed (Scheme 1, route b). [5][6][7] In addition, we recently disclosed an unprecedented ruthenium-catalyzed coupling between secondary alcohols E and primary alcohols B which leads to secondary alcohols C (Scheme 1, route c).8 Prompted by these findings, 9 we have directed our attention to the extension of this alkylation (Scheme 1, route b). Herein we report a ruthenium-catalyzed efficient direct synthesis of β-ferrocenylketones from ferrocenemethanol and ketones. 10 The results of several attempted couplings between ferrocenemethanol (1) and acetophenone (2a) are listed in Table 1. Treatment of equimolar amounts of 1 and 2a in dioxane in the presence of RuCl 2 (PPh 3 ) 3 (5 mol%) and KOH (3 equiv) at 80 o C for 24 h afforded 3-ferrocenyl-1-phenylpropan-1-one (3a) in 58% isolated yield with concomitant formation of 3-ferrocenyl-1-phenylpropenone (4, 14%) (entry 1).11 When the reaction was carried out at room temperature, 3a was obtained in only 30% yield even for a longer reaction time (43 h ) showed no significant change (entries 3 and 4). We previously reported that a hydrogen acceptor triggers the increase of reactivity and selectivity in the ruthenium-catalyzed coupling between ketones (or secondary alcohols) and primary alcohols. 5,8 However, as can be seen from entry 5, the selectivity of 3a/4 was not affected by the presence of the hydrogen acceptor and the yield of 4 showed no significant change.Given these results, the reactions between 1 and various ketones 2 were screened in order to synthesize a wide range of β-ferrocenylketones 3 (Table 2). Alkyl aryl ketones (2a-2j) were readily reacted with 1 to give the corresponding β-ferrocenylketones (3a-3j) in the range of 20-77% yields. The yield of 3 was affected by the position and electronic nature of the substituent on the aromatic ring of the ketones 2a-2j.With meta-and para-substituted ketones, the product yield was higher than that with ortho-substituted ketones (2b, 2e and 2g). With ketones (2h and 2i) having electron-withdrawing substituents such as 4-fluoro and 3-trifluoromethyl, the product yield was lower than that when ketones having electron-donating substituents such as methyl and methoxy were employed. In cases of dialkyl ketones (2k-2m), the alkylation took place exclusively at the less-hindered methyl position over α-...

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“…Similar regioselectivity was observed by others 12 and in our recent reports. 4,5,8,13 A possible reaction pathway based on our recent reports, 4,8 …”

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An Efficient Direct Synthesis of β-Ferrocenylketones Catalyzed by Ruthenium

2004

Bulletin of the Korean Chemical Society

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“…The quinoline skeleton is generally constructed by conventional named routes such as Skraup, Döbner-von Miller, Conrad-Limpach, Friedlaender and Pfitzinger syntheses.1 However, homogeneous transition metal-catalyzed versions have been introduced recently for the synthesis of quinolines because of facility and efficiency of reaction and wide availability of substrate.2 In our studies of ruthenium-catalyzed organic syntheses, [3][4][5][6][7][8][9][10][11][12][13] we have also developed on the rutheniumcatalyzed synthesis of quinolines by an alkyl group transfer from alkylamines to the nitrogen atom of anilines (amine exchange reaction or amine scrambling reaction 14 )5-8 and an oxidative cyclization of 2-aminobenzyl alcohol with ketones (modified Friedlaender synthesis).9 Prompted by the amine exchange reaction, we have directed our attention to the use of nitroarenes instead of anilines for the synthesis of Nheterocycles under our precedented ruthenium catalyst systems since nitroarenes are precursors of anilines from the viewpoint of industrial organic chemistry.15,16 Herein we report a ruthenium-catalyzed reductive N-heteroannulation of nitroarenes with tetraalkylammonium bromides leading to quinolines via an amine exchange reaction.Treatment of nitrobenzene (1a) with tetrabutylammonium bromide (2a) in the presence of a catalytic amount of RuCl 2 -(PPh 3 ) 3 (3 mol% based on 2a) along with SnCl 2 ·2H 2 O in dioxane at 180 o C for 20 h afforded the reductive cyclization product, 3-ethyl-2-propylquinoline (3a) in 67% GLC yield (based on 2a) with concomitant formation of aniline and Nbutylaniline (12% based on 2a). The addition of SnCl 2 ·2H 2 O was necessary for the effective formation of 3a and complete conversion of 1a (Eq.…”

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“…2 In our studies of ruthenium-catalyzed organic syntheses, [3][4][5][6][7][8][9][10][11][12][13] we have also developed on the rutheniumcatalyzed synthesis of quinolines by an alkyl group transfer from alkylamines to the nitrogen atom of anilines (amine exchange reaction or amine scrambling reaction 14 )…”

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confidence: 99%

“…1 However, homogeneous transition metal-catalyzed versions have been introduced recently for the synthesis of quinolines because of facility and efficiency of reaction and wide availability of substrate. 2 In our studies of ruthenium-catalyzed organic syntheses, [3][4][5][6][7][8][9][10][11][12][13] we have also developed on the rutheniumcatalyzed synthesis of quinolines by an alkyl group transfer from alkylamines to the nitrogen atom of anilines (amine exchange reaction or amine scrambling reaction 14 ) 5-8 and an oxidative cyclization of 2-aminobenzyl alcohol with ketones (modified Friedlaender synthesis). 9 Prompted by the amine exchange reaction, we have directed our attention to the use of nitroarenes instead of anilines for the synthesis of Nheterocycles under our precedented ruthenium catalyst systems since nitroarenes are precursors of anilines from the viewpoint of industrial organic chemistry.…”

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Ruthenium-Catalyzed Consecutive Reduction and Cyclization of Nitroarenes with Tetraalkylammonium Bromides Leading to Quinolines

2002

Bulletin of the Korean Chemical Society

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It is known that several quinoline containing compounds exhibit pharmacological activity for malaria. The quinoline skeleton is generally constructed by conventional named routes such as Skraup, Döbner-von Miller, Conrad-Limpach, Friedlaender and Pfitzinger syntheses.1 However, homogeneous transition metal-catalyzed versions have been introduced recently for the synthesis of quinolines because of facility and efficiency of reaction and wide availability of substrate.2 In our studies of ruthenium-catalyzed organic syntheses, [3][4][5][6][7][8][9][10][11][12][13] we have also developed on the rutheniumcatalyzed synthesis of quinolines by an alkyl group transfer from alkylamines to the nitrogen atom of anilines (amine exchange reaction or amine scrambling reaction 14 )5-8 and an oxidative cyclization of 2-aminobenzyl alcohol with ketones (modified Friedlaender synthesis).9 Prompted by the amine exchange reaction, we have directed our attention to the use of nitroarenes instead of anilines for the synthesis of Nheterocycles under our precedented ruthenium catalyst systems since nitroarenes are precursors of anilines from the viewpoint of industrial organic chemistry.15,16 Herein we report a ruthenium-catalyzed reductive N-heteroannulation of nitroarenes with tetraalkylammonium bromides leading to quinolines via an amine exchange reaction.Treatment of nitrobenzene (1a) with tetrabutylammonium bromide (2a) in the presence of a catalytic amount of RuCl 2 -(PPh 3 ) 3 (3 mol% based on 2a) along with SnCl 2 ·2H 2 O in dioxane at 180 o C for 20 h afforded the reductive cyclization product, 3-ethyl-2-propylquinoline (3a) in 67% GLC yield (based on 2a) with concomitant formation of aniline and Nbutylaniline (12% based on 2a). The addition of SnCl 2 ·2H 2 O was necessary for the effective formation of 3a and complete conversion of 1a (Eq. 1 and Table 1). Performing the reaction in the absence of SnCl 2 ·2H 2 O resulted in incomplete conversion of 1a (51%) and lower yield of 3a (24%). It is well-known that nitroarenes can be easily converted into anilines in the presence of SnCl 2 ·2H 2 O under nonacidic and nonaqueous media. 17 However, as has been observed in our recent report on the ruthenium-catalyzed synthesis of indoles and quinolines from anilines and alkylamines, another feature of SnCl 2 ·2H 2 O seems to play a decisive role in either alkyl group transfer or heteroannulation step.3-8 Interestingly, although 3a was produced in only 24% yield, much more N-butylaniline (54% based on 2a) was formed under the employment of an aqueous solvent system (dioxane/H 2 O = 9 mL/1 mL) in place of dioxane.The several attempted reductive N-heteroannulations of nitroarenes 1 with tetraalkylammonium bromides 2 leading to quinolines 3 are listed in Table 1. The quinoline yield was considerably affected by the position of the substituent on nitroarene. With meta-and para-substituted nitroarenes (1b and 1c), the quinoline yield was higher than that with orthosubstituted nitroarene 1d. In the case of 3-nitrotoluene (1c), the corresponding ...

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