Trihydroborates and Dihydroboranes Bearing a Pentacoordinated Phosphorus Atom: Double Ring Expansion To Balance the Coordination States.

The first trihydroborate bearing a pentacoordinated phosphorus atom was synthesized as a new P-B bonded compound. Hydride abstraction of the trihydroborate gave an intermediary dihydroborane, which showed hydroboration reactivity and was trapped with pyridine whilst maintaining the P-B bond. The dihydroborane underwent a rearrangement, which involved a double ring expansion to compensate for the unbalanced coordination states of the phosphorus and boron atoms, to give a new fused bicyclic phosphine-boronate.

Mechanism of Metal-Free C-H Activation of Branched Aldehydes and Acylation of Alkenes Using Hypervalent Iodine Compound: A Theoretical Study.

The mechanism of the C-H activation of aldehydes and the succeeding acylation of an alkene using a hypervalent iodine reagent is investigated by theoretical calculations. In contrast to the initial proposed mechanism, the present calculations show that the hypervalent iodine is the initiator of the radical reaction. The formation of acyl radical is rate-determining, and the resulting radical acts as the chain carrier.

Rh(III) -catalyzed C(sp(3))-H bond activation by an external base metalation/deprotonation mechanism: a theoretical study.

The C(sp(3) )H bond activation of 8-methylquinoline followed by alkyne insertion catalyzed by a Rh(III) complex has been studied by using density functional theory (DFT) calculations. Contrary to common belief, the CH bond activation of methylquinoline does not occur by the traditional intramolecular concerted metalation/deprotonation (CMD) mechanism but by an external base CMD mechanism. The use of free acetate or copper(II) acetate as base permits the CH activation step, as observed experimentally.

The Biginelli Reaction Is a Urea-Catalyzed Organocatalytic Multicomponent Reaction.

The recently developed artificial force induced reaction (AFIR) method was applied to search systematically all possible multicomponent pathways for the Biginelli reaction mechanism. The most favorable pathway starts with the condensation of the urea and benzaldehyde, followed by the addition of ethyl acetoacetate. Remarkably, a second urea molecule catalyzes nearly every step of the reaction.

Revisiting the Passerini reaction mechanism: existence of the nitrilium, organocatalysis of its formation, and solvent effect.

The Passerini reaction mechanism is revisited using high-level DFT calculations. Contrary to the common belief, the nitrilium intermediate is found to be stable in solution and its formation is rate-determining. The present results point out that this step is catalyzed by a second carboxylic acid molecule, as the subsequent Mumm rearrangement is.

Predicting new Ugi-smiles couplings: a combined experimental and theoretical study.

Following our previous mechanistic studies of multicomponent Ugi-type reactions, theoretical calculations have been performed to predict the efficiency of new substrates in Ugi-Smiles couplings. First, as predicted, 2,4,6-trichlorophenol experimentally gave the corresponding aryl-imidate. Theoretical predictions of nitrosophenols as good acidic partners were then successfully confirmed by experiments.

Substituent effects in Ugi-smiles reactions.

In a recent communication, we described the mechanism of the well-known Ugi-type reactions with a model system (J. Org. Chem.

Challenging 50 years of established views on Ugi reaction: a theoretical approach.

The Ugi reaction is one of the most famous multicomponent couplings, and its efficiency is still explained by the original mechanism suggested by Ugi in the 60s. This article aims to present a thorough theoretical study of this reaction. It describes how the imine is activated and how the new stereogenic center is formed.

The physical origin of large covalent-ionic resonance energies in some two-electron bonds.

This study uses valence bond (VB) theory to analyze in detail the previously established finding that alongside the two classical bond families of covalent and ionic bonds, which describe the electron-pair bond, there exists a distinct class of charge-shift bonds (CS-bonds) in which the fluctuation of the electron pair density plays a dominant role. Such bonds are characterized by weak binding, or even a repulsive, covalent component, and by a large covalent-ionic resonance energy RE(cs) that is responsible for the major part, or even for the totality, of the bonding energy. In the present work, the nature of CS-bonding and its fundamental mechanisms are analyzed in detail by means of a VB study of some typical homonuclear bonds (H-H, H3C-CH3, H2N-NH2, HO-OH, F-F, and Cl-Cl), ranging from classical-covalent to fully charge-shift bonds.