A Mitsunobu-based procedure for the preparation of alkyl and hindered aryl isocyanates from primary amines and carbon dioxide under mild conditions

Use of carbon dioxide as a reagent in place of phosgene offers the potential for an inexpensive, safer, and more selective route to polyurethanes. Traditionally, isocyanates, which are used for the production of polyurethanes, are generated from the reaction of a primary amine with the highly toxic agent phosgene. The reaction of CO2 with either primary or secondary amines generates the carbamate anion. By understanding those factors which control the nucleophilicity of the carbamate anion, we have been able to generate urethanes quantitatively even with secondary amine-derived carbamate anions. We have also found that isocyanates can be generated quantitatively by the "dehydration" of carbamate anions derived from primary amines and carbon dioxide using a variety of dehydrating reagents. These processes are accomplished under very mild conditions; e. g., 1 atm CO2 at 50-80°C. The factors which favor production of urethane or carbamate are discussed and examples of the utility of these new chemistries are presented.

Diarylation of N- and O-nucleophiles through a metal-free cascade reaction

Treatment of amines under a carbon dioxide atmosphere with tetramethylphenylguanidine (PhTMG) and diphenylphosphoryl azide (DPPA) in acetonitrile below 0 degrees C provides carbamoyl azides in high to excellent yields. In addition, epimerization is not observed when optically pure alpha-amino esters are used as substrates.

Treatment of primary amines with tetramethylphenylguanidine (PhTMG) and a cyanophosphonate at -10 degrees Celsius under an atmosphere of carbon dioxide provides cyanoformamides in very high to excellent yields. The reaction proceeds efficiently within a short time. By-products were not detected in most runs and epimerization was not found when optically pure alpha-aminoesters were used as substrates. As an example, the reaction was applied to the synthesis of the marine natural product ceratinamine.

The formation of C N bonds is one of the most important transformations in chemistry because nitrogen-containing compounds, particularly amines and their derivatives, are versatile building blocks for various organic molecules and essential precursors to a variety of biologically active compounds. Although several methods are known for the synthesis of C N bonds, preparation under mild and wastefree conditions using simple, inexpensive, and readily available feedstock is still a challenging goal. The transitionmetal-catalyzed coupling of amines with alcohols by using a hydrogen-borrowing strategy (also known as a hydrogenautotransfer process) has proven to be an atom-economical and environmentally attractive method for the construction of C N bonds, especially for secondary amine preparation. Although many efficient catalysts for such transformations have been reported, 4] the development of easily recoverable and recyclable heterogeneous catalysts that can solve the problem of the homogeneous systems has attracted special attention. To the best of our knowledge, few heterogeneous catalyst systems have been reported that enable efficient and selective N-alkylation of amines with alcohols under simple, mild, and environmentally benign conditions. Nitroarenes are cheap and readily available organic compounds and the reduction of nitro compounds is a key step in the preparation of many pharmaceutical agents and fine chemicals. Despite numerous established procedures for the reduction of nitro compounds, the development of catalytic methodologies that afford high chemoand regioselectivity under mild reaction conditions is still a challenging problem. As for the synthesis of secondary amines, the direct use of commercially available and inexpensive nitroarenes and alcohols as starting materials is highly attractive, especially when a single catalyst system could be employed. In this valuable one-pot multistep transformation, the alcohol may conceivably serve two possible functions: as the hydrogen source for nitro reduction and as the alkylating reagent based on the catalytic hydrogen transfer. Although excess alcohol is required to ensure the completion of the reaction (see the Supporting Information for possible reaction stoichiometries), the operational simplicity of such transformations may have practical advantages for a concise synthesis of N-substituted amines in a more straightforward manner. Compared to the great progress being made in the amination of amines with alcohols, there are scarcely available reports dealing with the direct amination of nitroarenes with alcohols. To date, only three Ru-based homogeneous systems have been reported. However, these homogeneous catalysts are problematic in terms of the recovery/ recycling of the catalyst and the necessity of special handling of metal complexes. From a sustainable point of view, a more efficient reaction with a ligand-free heterogeneous catalyst is highly desired. Over the last five years, we have been interested in the unique catalytic properties of supported gold nanoparticles (NPs) and involved in their application to sustainable organic synthesis. Recently, we have shown that very small Au NPs (approx. 1.8 nm) deposited on TiO2 (Au/TiO2-VS; VS=very small) acts as an efficient heterogeneous catalyst for the clean and atom-efficient mono-N-alkylation of a range of amines with alcohols in excellent yields under hydrogen-borrowing conditions. In view of the prominent efficiency of the gold system for the amination of amines with alcohols, we envisioned that the Au-mediated hydrogen-borrowing strategy could afford a green and efficient protocol for the direct amination of nitroarenes with alcohols under mild conditions. Herein, we report for the first time that the simple Au/TiO2-VS system can catalyze the selective secondary or tertiary amine formation from the direct condensation of nitroarenes and alcohols. Notably, the reaction can proceed effectively under ligandand basefree conditions without any external hydrogen resources. To the best of our knowledge, this study also forms the first report of a one-pot selective preparation of imines from nitroarenes and alcohols by using a heterogeneous gold-mediated “catalytic hydrogen-transfer” procedure. Based on our previous results in heterogeneous Au-catalyzed amine/alcohol coupling chemistry, the optimization study was initiated with the direct amination of nitrobenzene (1a) with eight equivalents of benzyl alcohol (2a) in the presence of Au/TiO2-VS (0.5 mol% of Au, see the Sup[a] C.-H. Tang, L. He, Dr. Y.-M. Liu, Prof. Dr. Y. Cao, Prof. Dr. H.-Y. He, Prof. K.-N. Fan Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials Department of Chemistry, Fudan University Shanghai 200433 (P.R. China) Fax: (+86)21-65643774 E-mail : yongcao@fudan.edu.cn Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201100393.

Synergistic CO2 Mediation and Photocatalysis for α-Alkylation of Primary Aliphatic Amines

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

High efficient copper-promoted N-arylation of secondary and primary amines with triarylbismuth reagents under mild conditions

Carbamate anions, derived from primary amines CO2 and an added base (e.g. NEt3), undergo rapid reaction with electrophilic ‘dehydrating agents’(e.g. POCl3, P4O10) to give the corresponding isocyanates in excellent yields.

Noble metal free double helix binuclear Cu(I) complex as catalyst for carboxylative cyclization of propargylamines with atmospheric carbon dioxide toward oxazolidinones synthesis under mild conditions

A new ruthenium catalytic system for the syntheses of secondary and tertiary amines via reductive N‐alkylation of nitriles and N‐alkylation of primary amines is proposed. Isomeric complexes 8 catalyze transfer hydrogenation and N‐alkylation of nitriles in ethanol to give secondary amines. Unsymmetrical secondary amines can be produced by N‐alkylation of primary amines with alcohols via the borrowing hydrogen methodology. Aliphatic amines were obtained with excellent yields, while only moderate conversions were observed for anilines. Based on kinetic and mechanistic studies, it is suggested that the rate determining step is the hydrogenation of intermediate imine to amine. Finally, ammonium formate was applied as the amination reagent for alcohols in the presence of ruthenium catalyst 8. Secondary amines were obtained from primary alcohols within 24 hours at 100 °C, and tertiary amines can be produced after prolonged heating. Secondary alcohols can only be converted to secondary amines with moderate yield. Based on mechanistic studies, the process is suggested to proceed through an ammonium alkoxy carbonate intermediate, where carbonate acts as an efficient leaving group.

Visible-light photoredox-catalyzed selective carboxylation of C(sp3)−F bonds with CO2

Boosting CO2 Conversion with Terminal Alkynes by Molecular Architecture of Graphene Oxide-Supported Ag Nanoparticles

Tertiary Amine Synthesis by Radical Carbonyl Alkylative Amination