Tuning the Reactivity of a Heterogeneous Catalyst using N-Heterocyclic Carbene Ligands for C−H Activation Reactions

We report the dramatic impact of the addition of N-heterocyclic carbenes (NHCs) on the reactivity and selectivity of heterogeneous Ru catalysts in the context of C−H activation reactions. Using a simple and robust method, we prepared a series of new air-stable catalysts starting from commercially available Ru on carbon (Ru/C) and differently substituted NHCs. Associated with C−H deuteration processes, depending on Ru/C-NHC ratios, the chemical outcome can be controlled to a large extent. Indeed, tuning the reactivity of the Ru catalyst with NHC enabled: 1) increased chemoselectivity and the regioselectivity for the deuteration of alcohols in organic media; 2) the synthesis of fragile pharmaceutically relevant deuterated heterocycles (azine, purine) that are otherwise completely reduced using unmodified commercial catalysts; 3) the discovery of a novel reactivity for such heterogeneous Ru catalysts, namely the selective C-1 deuteration of aldehydes.     

An Unexpected Transannular [4+2] Cycloaddition during the Total Synthesis of (+)‐Norcembrene 5

We report a concise and versatile total synthesis of the diterpenoid (+)‐norcembrene 5 from simple building blocks. Ring‐closing metathesis and an auxiliary‐directed 1,4‐addition are the key steps of our synthetic route. During the synthesis, an unprecedented, highly oxidized pentacyclic structural motif was established from a furanocembranoid through transannular [4+2] cycloaddition.     

Enantioselective straightforward access to benzo[b]thiophene analogs of Azatoxin

Horner-Wadsworth Emmons olefination followed by asymmetric hydrogenation allowed the first synthetic access to the chiral thiotryptophan with good enantiomeric excess. Oxazolidinone formation followed by a Pictet–Spengler condensation provided the benzothiophenic analog of Azatoxin.     

Measurement of traffic noise shielding provided by buildings

This paper presents a comparison between some current prediction methods for traffic noise shielding provided by buildings and the actual measured attenuations in typical residential areas. Generally, it was found that the method developed by the Department of Environment in the UK gives a reasonably accurate prediction of attenuation by shielding in fairly simple situations. In more complex situations, and particularly where a receiving position is close to a significant shielding structure, such as building, the attenuation obtained is underpredicted by the DOE method, thus the design facade levels for the rear of a building are overpredicted; however, in some other situations, the DOE method overpredicts the attenuation obtained. The attenuations measured for individual noise events under nominally identical conditions are shown to have large variations in attenuation.