/pdf/aryl-aryl-bond-formation-one-century-after-the-discovery-of-1jdyxlkwix.pdf

Aryl-aryl bond formation one century after the discovery of the Ullmann reaction.

N-Heterocyclic Carbenes in Late Transition Metal Catalysis

Catalysis for the valorization of exhaust carbon: from CO2 to chemicals, materials, and fuels. technological use of CO2.

A new iron(III) halide-promoted aza-Prins cyclization between γ,δ-unsaturated tosylamines and aldehydes provides six-membered azacycles in good to excellent yields. The process is based on the consecutive generation of γ-unsaturated-iminium ion and further nucleophilic attack by the unsaturated carbon−carbon bond. Homoallyl tosylamine leads to trans-2-alkyl-4-halo-1-tosylpiperidine as the major isomer. In addition, the alkyne aza-Prins cyclization between homopropargyl tosylamine and aldehydes gives 2-alkyl-4-halo-1-tosyl-1,2,5,6-tetrahydropyridines as the only cyclic products. The piperidine ring is widely distributed throughout Nature, e.g., in alkaloids,1 and is an important scaffold for drug discovery, being the core of many pharmaceutically significant compounds.2,3 The syntheses of these type of compounds have been extensively studied in the development of new drugs containing six-membered-ring heterocycles.4 Reactions between N-acyliminium ions and nucleophiles, also described as amidoalkylation or Mannich-type condensations, have been frequently used to introduce substituents at the R-carbon of an amine.5 There are several examples that involve an intramolecular attack of a nucleophilic olefin into an iminium cation for the construction of a heterocyclic ring system.6 Traditionally, the use of hemiaminals or their derivatives as precursors of N-acyliminium intermediates has been a common two-step strategy in these reactions.6a Among this type of cyclization is the aza-Prins cyclization,7 which uses alkenes as intramolecular nucleophile. However, cy† X-ray analysis. E-mail address: malopez@ull.es. (1) (a) Fodor, G. B.; Colasanti, B. Alkaloids: Chemical and Biological PerspectiVes; Pelletier, S. W., Ed.; Wiley: New York, 1985; Vol. 23, pp 1-90. (b) Baliah, V.; Jeyarama, R.; Chandrasekaran, L. Chem. ReV. 1983, 83, 379-423. (2) Watson, P. S.; Jiang, B.; Scott, B. Org. Lett. 2000, 2, 3679-3681. (3) Horton, D. A.; Bourne, G. T.; Smythe, M. L. Chem. ReV. 2003, 103, 893-930. (4) Buffat, M. G. P. Tetrahedron 2004, 60, 1701-1729 and references therein. (5) Speckamp, W. N.; Moolenaar, M. J. Tetrahedron 2000, 56, 3187- 3856 and references therein. (6) (a) Hiemstra, H.; Speckamp, W. N. In ComprehensiVe Organic Synthesis; Trost, B. M., Fleming, O., Heathcock, C. H., Eds.; Pergamon: New York, 1991; Vol. 2, pp 1047-1081. (b) Speckamp, W. N.; Hiemstra, H. Tetrahedron 1985, 41, 4367-4416. (7) (a) Dobbs, A. P.; Guesne, S. J. J.; Hursthouse, M. B.; Coles, S. J. Synlett 2003, 11, 1740-1742. (b) Dobbs, A. P.; Guesne, S. J. J.; Martinove, S.; Coles, S. J.; Hursthouse, M. B. J. Org. Chem. 2003, 68, 7880-7883. (c) Hanessian, S.; Tremblay, M.; Petersen, F. W. J. Am. Chem. Soc. 2004, 126, 6064-6071 and references therein. (d) Dobbs, A. P.; Guesne, S. J. Synlett 2005, 13, 2101-2103. ORGANIC

Iron-Catalyzed Reactions in Organic Synthesis

Carbon dioxide exits in the atmosphere and is produced by the combustion of fossil fuels, the fermentation of sugars and the respiration of all living organisms. An active goal in organic synthesis is to take this carbon--trapped in a waste product--and re-use it to build useful chemicals. Recent advances in organometallic chemistry and catalysis provide effective means for the chemical transformation of CO₂ and its incorporation into synthetic organic molecules under mild conditions. Such a use of carbon dioxide as a renewable one-carbon (C1) building block in organic synthesis could contribute to a more sustainable use of resources.

/pdf/using-carbon-dioxide-as-a-building-block-in-organic-4s0h674ulv.pdf

Using carbon dioxide as a building block in organic synthesis

Carbon dioxide (CO2) is an attractive, cheap, and nontoxic C1 source. However, because of its high thermodynamic stability and low reactivity, the use of CO2 as a C1 source for C C bond formation usually requires highly nucleophilic organometallic reagents, such as alkyllithium compounds and Grignard reagents. Less nucleophilic organoboron compounds, though easily available, usually do not react with CO2. Recently, transition-metal-catalyzed addition of carbon nucleophiles to CO2 has attracted much attention. [2,3] In this context, Iwasawa and co-workers have reported the catalytic carboxylation of aryland alkenylboronic esters with CO2 in the presence of a rhodium(I) compound and additives. This reaction is potentially useful for the synthesis of functionalized carboxylic acid derivatives because of the easy availability of various functionalized organoboronic esters. Unfortunately, however, the Rh catalyst systems showed only limited tolerance toward functional groups. Although carbonyl and cyano groups survived the reaction conditions, more reactive functional moieties, such as bromo, iodo, and vinyl groups, seemed intolerant. Moreover, little information about the active catalyst species and the reaction mechanism was available because of the complexity of the catalyst systems. These difficulties have limited the application scope of the Rh catalyst systems. The search for new catalysts for more efficient, selective CO2 transformation as well as the clarification of the catalytic process is therefore of interest and importance. We report herein an excellent N-heterocyclic carbene copper(I) catalyst system for the carboxylation of aryland alkenylboronic esters with CO2. This Cu catalyst system not only showed higher functional-group tolerance, but could also afford structurally characterizable active catalyst species, thus offering unprecedented insight into the mechanistic aspects of the catalytic process. Copper complexes bearing N-heterocyclic carbene (NHC) ligands have been reported to act as efficient catalysts for the transformation of various carbonyl compounds, such as conjugate reduction of a,b-unsaturated carbonyl compounds, hydrosilylation of ketones, and also for the reduction of CO2. [7] In addition, many copper compounds have also been reported to promote nucleophilic addition of organoboron compounds to electrophiles, such as a,b-unsaturated carbonyls and allylic carbonates. These results encouraged us to examine the carboxylation of organoboronic esters with CO2 by use of N-heterocyclic carbene copper complexes as catalysts. At first we examined the reaction of 4methoxyphenylboronic acid 2,2-dimethyl-1,3-propanediol ester (1a) with CO2 using N-heterocyclic carbene copper species generated in situ from CuCl, IPr·HCland tBuOK. In

Carboxylation of Organoboronic Esters Catalyzed by N‐Heterocyclic Carbene Copper(I) Complexes

The use of carbon dioxide (CO2) as a C1 building block for chemical synthesis has recently attracted much interest because of its abundance, low cost, nontoxicity, and high potential as a renewable source. However, the high thermodynamic stability and low reactivity of CO2 means that its use in C C bond-forming reactions usually requires organometallic reagents or other preactivated substrates such as organic halides (Scheme 1, routes a and b). Although the reaction of C H bonds with CO2 would be the most attractive and atom-economic route for the synthesis of carboxylic acids (Scheme 1, route c), the direct carboxylation of a C H bond with CO2 has remained a challenge. [4]

Copper‐Catalyzed Direct Carboxylation of CH Bonds with Carbon Dioxide

Caught in the act: N-Heterocyclic carbene copper(I) complexes (1; IPr=1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) serve as an excellent catalyst for the carboxylation of alkylboranes (2; R=alkyl) with CO(2) to afford a variety of functionalized carboxylic acids (3) in high yields. A novel copper methoxide/alkylborane adduct (A) and its subsequent CO(2) insertion product (B) have been isolated and shown to be true active catalyst species.

Carboxylation of Alkylboranes by N‐Heterocyclic Carbene Copper Catalysts: Synthesis of Carboxylic Acids from Terminal Alkenes and Carbon Dioxide

Trifluoromethanesulfonic Acid, an Unusually Powerful Catalyst for the Michael Addition Reaction of beta-Ketoesters under Solvent-Free Conditions.

High-yielding TfOH-catalyzed condensation of phenols with aromatic aldehydes at high pressure. A model synthesis of the benzylidene biphenol key skeleton of blepharismins

Takeshi Ohishi

Papers

Carboxylation of Organoboronic Esters Catalyzed by N‐Heterocyclic Carbene Copper(I) Complexes

Copper‐Catalyzed Direct Carboxylation of CH Bonds with Carbon Dioxide

Carboxylation of Alkylboranes by N‐Heterocyclic Carbene Copper Catalysts: Synthesis of Carboxylic Acids from Terminal Alkenes and Carbon Dioxide

Trifluoromethanesulfonic Acid, an Unusually Powerful Catalyst for the Michael Addition Reaction of beta-Ketoesters under Solvent-Free Conditions.

High-yielding TfOH-catalyzed condensation of phenols with aromatic aldehydes at high pressure. A model synthesis of the benzylidene biphenol key skeleton of blepharismins