NHC-Organocatalyzed CAr -O Bond Cleavage: Mild Access to 2-Hydroxybenzophenones.

A Truce-Smiles rearrangement of acyl-anion equivalents generated by N-heterocyclic carbene (NHC) catalysis has been achieved. The developed method includes CAr -O, CAr -S, or CAr -N bond cleavage for the formation of a CAr -C bond and enables access to 2-hydroxybenzophenones, an important structural motif that is present in several bioactive natural products. By utilizing this procedure, the alkaloid taxilamine was synthesized in three steps. DFT calculations and control experiments support a classical SN Ar mechanism with a catalyst-bound Meisenheimer-type intermediate. The method features mild reaction conditions, excellent functional-group tolerance, and a broad substrate scope, including various classes of (hetero)arenes.

Dual role of Rh(III) catalyst enables regioselective halogenation of (electron-rich) heterocycles.

The Rh(III)-catalyzed selective bromination and iodination of electron-rich heterocycles is reported. Kinetic investigations show that Rh plays a dual role in the bromination, catalyzing the directed halogenation and preventing the inherent halogenation of these substrates. As a result, this method gives highly selective access to valuable halogenated heterocycles with regiochemistry complementary to those obtained using uncatalyzed approaches, which rely on the inherent reactivity of these classes of substrates. Furans, thiophenes, benzothiophenes, pyrazoles, quinolones, and chromones can be applied.

Preparation of conjugated 1,3-enynes by Rh(III)-catalysed alkynylation of alkenes via C-H activation.

An experimentally simple additive-free Rh(III)-catalysed direct alkynylation of alkenes has been developed. This protocol employs commercially available TIPS-EBX as the alkyne source, giving access to conjugated terminal enynes following a simple silyl-deprotection. This method has also been applied to arenes.

Rapid assessment of protecting-group stability by using a robustness screen.

An experimentally simple method has been developed to rapidly establish the stability of widely utilized silyl, acetal, and carbamate protecting groups to a given set of reaction conditions. Assessment of up to twelve protecting groups in a single experiment has been demonstrated. Evaluation of this protocol in two unrelated synthetic transformations suggests that this method can be used to select appropriate protecting groups in the design of synthetic routes.

Pattern formation of anisotropic molecules on surfaces under non-equilibrium conditions as described by a minimum model.

The self-organization of lipophilic chain molecules on surfaces in vacuum deposition experiments has been recently studied by Monte Carlo simulations of a coarse grained microscopic model system. Surprisingly, the final potential energy depends in a non-monotonous way on the chosen flux and the surface temperature. Here we introduce a schematic model which contains the relevant physical ingredients of the microscopic model and which elucidates the origin of this anomalous non-equilibrium effect. Intra-cluster effects, reflecting the chain arrangement within one cluster, and inter-cluster effects, based on the distribution of chains among the different formed clusters, are taken into account. This schematic model is solved numerically as well as via analytical means. From the analytical solutions, it is possible to understand quantitatively for which interaction parameters the observed anomalies can indeed be observed. The generality of the observed phenomena is stressed. It is related to the concept of kinetic trapping, which often occurs during self-assembly.

Different growth regimes on prepatterned surfaces: consistent evidence from simulations and experiments.

Molecule deposition on a prepatterned substrate is a recently developed technique to generate desired structures of organic molecules on surfaces via self-organization. For the case of prepatterned stripes, the time-resolved process of structure formation is studied via lattice Monte Carlo simulations. By systematic variation of the interaction strength, three distinct growth regimes can be identified: localized growth, bulge formation, and cluster formation. All three growth regimes can be recovered in the experiment when choosing appropriate organic molecules. Some key microscopic observables, reflecting the properties of the structure formation, display a non-monotonous dependence on the interaction strength.