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Carbene intermediates are very useful species for a range of reactions including C-H insertions and cycloadditions. They are most commonly generated by metal-catalyzed release of nitrogen gas from diazo precursors. Herein, we present a novel C-H insertion of simple β-ketoamide substrates, through reaction with (diacetoxyiodo)benzene (DIB) in the presence of a base. This unprecedented transformation bypasses the use of either diazo precursors or metal catalysts and directly delivers β-lactam products by an iodonium ylide, in a single step under mild conditions. Mechanistic studies support the intermediacy of a free singlet carbene of unique reactivity and selectivity.

A gold-catalyzed methylenecyclopropanation of amino-substituted allenes using diphenylsulfonium ylides derived from activated methylene compounds as an interesting safe alternative to diazo compounds is presented.

A sequential process for the Eistert ring expansion of isatins with ethyl diazoacetate is developed consisting of a DBU-promoted addition of the diazoester to the isatin 3-carboxy group followed by Rh(II)-catalyzed diazo decomposition of the isatin diazo intermediate.

Herein we demonstrate for the first time that a boron promoted one-pot assembly reaction may be used to discover novel enzyme inhibitors. Inhibitors for HNE were simply assembled in excellent yields, high diastereoselectivities and IC50 up to 1.10 μM, based on components like salicylaldehyde, aryl boronic acids and amino acids. The combination of synthetic, biochemical, analytical and theoretical studies allowed the identification of the 4-methoxy or the 4-diethyl amino substituent of the salicylaldehyde as the most important recognition moiety and the imine alkylation, lactone ring opening as key events in the mechanism of inhibition.

An innovative stereoselective synthesis of N-acylhydrazones via an unprecedented N-heterocyclic carbene catalyzed addition of aldehydes to diazo compounds is presented. Enals exclusively afforded N-acylhydrazones, in yields up to 91%. The observed regioselectivity was traced back to the reaction of the vinylogous Breslow intermediate via the acyl anion pathway over competing homoenolate, enol, and acyl azolium pathways. This unusual reaction profile was studied based on DFT calculations, which revealed that the reaction is under orbital control, rather than being ruled by charge.

Doubly stabilized sulfonium ylides undergo an intra- or intermolecular coupling reaction with alkynes in the presence of modified gold catalysts.

Over the years, dirhodium(II) complexes have had an important role in the synthesis of numerous complex organic molecules because many useful transformations are mediated by this unique family of complexes. The recognized success of this class of catalysts relies on their bimetallic structure. They have a Rh–Rh bond, two axial ligands, and four bridging ligands responsible for controlling the catalyst electrophilicity and, in some cases, provide a mechanism for inducing asymmetry. The modification of the bridge ligand structure has been the main strategy to prepare new complexes, whereas the axial ligands have been considered to have a less important role in catalysis. This concept is changing, and over the past decade, the axial ligand modification was proven to be a valuable and simple strategy to prepare new complexes and achieve new reactivities. In this review a comprehensive overview of this topic is presented, with a particular focus on the changes induced by the axial coordination on the complex p...

Title Fe—NHC-catalyzed oxidative esterification of phenols proceeds with a wide range of aromatic (I), (IV) as well as cinnamic aldehydes (VII) to give the corresponding benzoates and cinnamates in good yields.

An overview of the reactivity of coordinatively unsaturated iron complexes (in most cases Fe(II)) towards carbon monoxide is presented. Unsaturated iron complexes are known with coordination numbers (CN) of two to five adopting linear or slightly bent (CN = 2), trigonal (CN = 3), tetrahedral, square planar or trigonal pyramidal (CN = 4), and square-pyramidal or trigonal-bipyramidal geometries (CN = 5), respectively. The binding of CO depends strongly on the number and the nature of co-ligands (overall ligand field strength), the charge of the complex, the complex geometry, and the spin state of the unsaturated metal center. In many cases, CO addition to high-spin iron complexes takes place with concomitant spin state changes forming compounds in the lowest possible spin state, i.e., with S = 0. In several other cases, however, the addition of CO is reversible or is even totally rejected altogether for either thermodynamic or kinetic reasons. In the case of the latter such reactions are termed “spin-blocked” or “spin forbidden”.

The DABCO-catalyzed ring contraction of pyranones (I) is successfully coupled with the lipase-catalyzed dynamic kinetic resolution to give enantioenriched cyclopentenones (III) in a one-pot two step procedure.

Novel title ligands are designed and complex (I) is found to show enhanced activity in the arylation of aldehydes with boronic acids.

Iron trans-dicarbonyl pincer-type complexes are shown to catalyze the coupling of aromatic aldehydes with ethyl diazoacetate to give the products (III) or (V) resulting from an intermediate aryl-shift and the direct coupling products (VI).

Petasis-borono-Mannich reaction, using structurally different aldehydes such as salicylaldehyde, glyoxalic acid and glycoaldehyde is developed.

The ring slippage reaction, induced by ligand addition or by reduction, is an important reaction in organometallic chemistry, and has been theoretically studied in recent years, using ab initio methods, in several systems such as [Mo(r)5-XMn(CO)3] (X can be one among a wide variety of rings), [Mo(r)5-Ind)(CO)2(L)2]+ (L=CO, phosphite), [Mo(r)5-(r)5-Ind)L2)(L2]2+. The slippage process is driven by a tendency to decrease the antibonding character of the HOMO after two electrons are added to the system and, usually, a structural rearrangement of the complex (or the ring) takes place, depending on the characteristics of the polyene in the ring. Larger rings are found to slip more easily, although they don't fold, in opposition to what happens to indenyl in all examples known.

Water was used as the solvent in the Petasis borono-Mannich reaction. With the use of salicylaldehyde, secondary amines and boronic acids, several alkylaminophenols were obtained in considerably high yields in water. By using the same methodology, 2H-chromenes were prepared with the use of vinyl boronic acids. The reaction mechanism was studied by DFT calculations, and the results obtained corroborate the solvent effect experimentally observed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

An efficient new methodology for the arylation of aldehydes is disclosed which uses dirhodium(II) catalysts and N-heterocyclic carbene (NHC) ligands. Complexes of Rh-2(OAc)(4) with one and two NHCs attached on the axial positions were successfully isolated, fully characterized, and used as catalysts in the reaction. The saturated monocomplex ((NHC 5)Rh-2(OAc)(4)) 31 was shown to be the most active catalyst and was particularly efficient in the arylation of alkyl aldehydes. DFT calculations support participation of complexes with one axial NHC in the reaction as the catalysts active species and indicate that hydrogen bonds involving dirhodium unit, reactants, and solvent (alcohol) play an important role on the reaction mechanism.