Nuclear magnetic resonance spectroscopy. Carbon-13 chemical shifts in norbornyl derivatives

Desilylation-acetylation of Trimethylsilyl Ethers with Acetic Anhydride Catalysed by Montmorillonite K-10

Two mild and simple one-step desilylation-acetylations of a variety of alkyl- and aryl-trimethylsilyl ethers, Me3SiOR(Ar), with acetic anhydride in the presence of montmorillonite K-10 clay are described.

Probing Stereoselectivity in Ring-Opening Metathesis Polymerization Mediated by Cyclometalated Ruthenium-Based Catalysts: A Combined Experimental and Computational Study

The microstructures of polymers produced by ring-opening metathesis polymerization (ROMP) with cyclometalated Ru-carbene metathesis catalysts were investigated. A strong bias for a cis,syndiotactic microstructure with minimal head-to-tail bias was observed. In instances where trans errors were introduced, it was determined that these regions were also syndiotactic. Furthermore, hypothetical reaction intermediates and transition structures were analyzed computationally. Combined experimental and computational data support a reaction mechanism in which cis,syndio-selectivity is a result of stereogenic metal control, while microstructural errors are predominantly due to alkylidene isomerization via rotation about the Ru═C double bond.

Anti-tuberculosis Compounds from two Bolivian Medicinal Plants, Senecio Mathewsii and Usnea Florida

Bioassay-directed fractionation of the organic extract of Senecio mathewsii gave four compounds with anti-TB activity: werneria chromene (1), capillarol (2), werneria chromanone (3) and plicatin B (4). All of these are new to the genus Senecio and one of these, werneria chromanone (3), was isolated from a natural source for the first time. With the aid of 2D NMR, revised (1) or new (2–4) spectral assignments were made. Similarly, the major anti-TB activity of Usnea florida was shown to be solely due to usnic acid.

Thermal isomerization of (3-butenyl)cyclopropane to norbornane

[reaction: see text] (3-Butenyl)cyclopropane isomerizes thermally to norbornane and gives rise to many other products. Deuterium and carbon-13-labeled versions of (3-butenyl)cyclopropane have been prepared and isomerized, establishing that the formation of norbornane involves cleavage of the cyclopropyl C2-C3 bond.