Ruthenium-catalyzed oxidative coupling and cyclization between 2-aminobenzyl alcohol and secondary alcohols leading to quinolines

2-Aminobenzyl alcohol is oxidatively coupled and cyclized with secondary alcohols in dioxane at 80°C in the presence of a catalytic amount of RuCl₂(PPh₃)₃ and KOH along with 1-dodecene as a sacrificial hydrogen acceptor to give the corresponding quinolines in good yields. The cyclization is applicable to a wide range of alkyl(aryl) and alkyl(alkyl) carbinols. The catalytic pathway seems to be proceeded via a sequence involving initial oxidation of both substrates to carbonyl compounds, cross aldol reaction, and cyclodehydration.     

Effect of a proximal substituent on the triruthenium dodecacarbonyl-catalyzed reductive carbonylation of nitroarenes

Three nitroarenes were submitted to Ru₃(CO)₁₂-catalyzed reductive carbonylation in acetonitrile and in cis-cyclooctene. The main reaction products were the corresponding amines, ureas and six- or five-membered cyclization products. Optimization of the reaction varying the temperature, the CO pressure, the catalyst/substrate ratio and the reaction time and a statistical analysis of conversion and selectivity data allow to suggest a reaction mechanism in some reaction conditions.     

A straightforward approach to N-substituted-2H-indazol-2-amines through reductive cyclization

A versatile two-step, one-pot reaction to access N-substituted-2H-indazol-2-amine derivatives has been elaborated. A diverse set of analogues was obtained by a sequential hydrazone formation and reductive cyclization in moderate to good yields from readily available starting materials. The strategy tolerates a broad range of substitutions pattern and functional groups allowing further derivatizations.     

Stereoselective synthesis of substituted N-heterocycles via sequential cross metathesis—reductive cyclization

A diastereoselective synthesis of substituted mono- and bicyclic-piperidine and pyrrolidine derivatives is presented, employing a highly selective cross metathesis (CM) reaction followed by a domino reduction-cyclization process.     

The first reductive cyclization by lithium aluminum hydride: stereospecific reductive cyclization of 1-(methoxycarbonylmethyl)imidazolidin-4-ones

The first LiAlH₄-driven reductive cyclization of the bifunctional 1-(methoxycarbonylmethyl)imidazolidin-4-ones, (−)-1a-c or(+)-1a-c, stereospecifically generated the corresponding 1,6-diaza-4-oxa-bicyclo[3.2.1]octanes, (−)-3a-c or(+)-3a-c, with a novel bicyclic system.     

A highly active catalyst for the reductive cyclization of ortho-nitrostyrenes under mild conditions

A mild and efficient method for the palladium-catalyzed reductive cyclization of ortho-nitrostyrenes to afford indoles is reported. Treatment of ortho-nitrostyrenes with 0.1 mol% palladium (II) trifluoroacetate [Pd(TFA)₂] and 0.7 mol% 3,4,7,8-tetramethyl-1,10-phenanthroline (tm-phen) in DMF at 15 psig CO and 80 °C afforded indoles in good to excellent yields. When the reaction was conducted in toluene, the corresponding N-hydroxyindole was isolated. A mechanism that accounts for the formation of N-hydroxyindole is proposed.     

Reduction of nitroarenes followed by propanol group transfer from tris(3‐hydroxypropyl)‐ amine and cyclization leading to quinolines under heterogeneous Pd?C catalysis

Nitroarenes having electron‐donating or ‐withdrawing substituents are reduced to anilines and cyclized with tris(3‐hydroxypropyl)amine in the presence of a catalytic amount of Pd? C along with tin(II) chloride and isopropanol in dioxane‐H₂O medium to give the corresponding quinolines in good to excellent yields. Copyright © 2009 John Wiley & Sons, Ltd.     

Ruthenium-catalyzed addition of sulfenamides to alkynes leading to selective synthesis of polyfunctional alkenes

Sulfenamides smoothly add to alkynes by [RuCl₂(CO)₃]₂ or Ru₃(CO)₁₂ catalyst to give the corresponding polyfunctional alkenes in high yield with high regio- and stereoselectivity (Z 100%).     

A Pd[0]-catalyzed Ullmann cross-coupling/reductive cyclization approach to C-3 mono-alkylated oxindoles and related compounds

The Pd[0]-catalyzed Ullmann cross-coupling of o-nitrohaloarenes 1a-e with the brominated heterocycles 2a-f delivers the expected products 3a-j in good to excellent yields. The reductive cyclization of such products, as well as N-acyl derivatives 3k, l, and m, has been investigated and provided the C-3 mono-substituted oxindoles 5a-d, f, g, k, and m, the direct reduction products 4i and j or indole 5l.     

Double reductive cyclization: a facile synthesis of the indoloquinoline alkaloid cryptotackieine

A new synthesis of the indoloquinoline alkaloid cryptotackieine, isolated from Cryptolepis sanguinolenta, is described which involves a Perkin reaction, a tandem double reduction-double cyclization reaction followed by regioselective methylation at the quinoline nitrogen.     

One-pot reactions of bicyclic zinc enolate generated from Ni-catalyzed reductive cyclization to furnish octahydro-4,7-ethanobenzofuran-9-one derivatives

The one-pot reactions of catalytically generated bicyclic zinc enolate with various electrophiles are reported. The zinc enolate as a key intermediate is efficiently delivered from Ni-catalyzed reductive cyclization of alkynyl cyclohexadienone. Employing aldehydes, imine, nitroalkene, and α,β-unsaturated carbonyl compounds as electrophiles, this new class of one-pot reactions gave multi-functionalized cis-hydrobenzofurans and octahydro-4,7-ethanobenzofuran-9-one derivatives in moderate to good yields.     

Palladium-catalyzed carbonylative cyclization of 2-bromobenzaldehyde with primary amines leading to isoindolin-1-ones

2-Bromobenzaldehyde is carbonylatively cyclized with primary amines under carbon monoxide pressure in DMF at 100 °C in the presence of a catalytic amount of a palladium catalyst to give the corresponding isoindolin-1-ones in moderate to high yields.     

An unusual palladium-catalyzed carbonylative cyclization of β-bromovinyl aldehydes leading to lactones

β-Bromovinyl aldehydes are carbonylatively cyclized under carbon monoxide pressure in MeCN at 100 °C in the presence of a catalytic amount of a palladium catalyst along with a base to give the corresponding lactones in high yields.     

Iron-catalyzed cascade reaction of ynone with o-aminoaryl compounds: a Michael addition-cyclization approach to 3-carbonyl quinolines

An efficient iron-catalyzed cascade Michael addition-cyclization of o-aminoaryl compounds including o-aminoaryl aldehydes, o-aminoaryl ketones, and o-aminobenzyl alcohols with ynones for the synthesis of 3-carbonyl quinolines is reported. The reactions proceed to afford 3-carbonyl quinoline derivatives with or without substituent at the C-4 position in good to high yields using Iron(III) chloride hexahydrate as the catalyst in the air.     

Base-mediated synthesis of quinolines: an unexpected cyclization reaction between 2-aminobenzylalcohol and ketones

Quinolines are prepared in an oxidative cyclization reaction between 2-aminobenzylalcohol and ketones. This reaction, that involves a hydrogen transfer, is mediated solely by a base without the need for a transition metal catalyst.     

Ruthenium-catalyzed arylation of fluorinated aromatic ketones via ortho-selective carbon-fluorine bond cleavage

We report here ruthenium-catalyzed arylation of fluorinated aromatic ketones via ortho-selective carbon-fluorine bond cleavage. In the presence of trimethylvinylsilane and cesium fluoride, ortho carbon-fluoride bonds of aromatic ketones were phenylated by 5,5-dimethyl-2-phenyl-1,3,2-dioxaborinane using RuH₂(CO)(PPh₃)₃ as a catalyst. Tandem C-F phenylation/C-H alkylation was observed for substrates bearing both one ortho hydrogen and one ortho fluorine atoms.     

Ruthenium-catalyzed reaction of alkenyl triflates with zinc thiolates

A ruthenium complex coordinated with 3,4,7,8-tetramethyl-1,10-phenanthroline catalyzed the reaction of alkenyl triflates with zinc dithiolates to give alkenyl sulfides.     

Photochemical intramolecular cyclization of o-alkynylaryl isocyanides with organic dichalcogenides leading to 2,4-bischalcogenated quinolines

When a mixture of o-alkynylaryl isocyanides and organic dichalcogenides such as diselenides or ditellurides was irradiated with light of wavelength over 300 or 400 nm, the intramolecular cyclization of the isocyanides took place to afford the corresponding 2,4-bischalcogenated quinolines selectively. The photochemical cyclization of 2-(phenylethynyl)phenyl isocyanide could also proceed in the presence of hydrogen transfer reagents such as tris(trimethylsilyl)silane, tributylgermyl hydride, alkanethiols, and benzeneselenol, providing the corresponding 3-phenylquinoline as the result of 2,4-dihydrogenation.     

Acid-promoted cyclization of 2-propynolphenols leading to 4-tosyloxy-2H-chromenes

A novel and efficient p-TsOH-promoted cascade cyclization of 2-propynolphenols is developed to give 4-tosyloxy-2H-chromenes in moderate to efficient yields. It is noted that p-TsOH acts not only as a promoter in this reaction, and also as the sulfonate source. Importantly, the obtained 4-tosyloxy-2H-chromenes can be used as versatile intermediates for the synthesis of various functionalized compounds through diverse metal-catalyzed cross-coupling reactions. Moreover, this method can be enlarged to gram scale.