The Smelling Principle of Vetiver Oil, Unveiled by Chemical Synthesis.

Vetiver oil, produced on a multiton-scale from the roots of vetiver grass, is one of the finest and most popular perfumery materials, appearing in over a third of all fragrances. It is a complex mixture of hundreds of molecules and the specific odorant, responsible for its characteristic suave and sweet transparent, woody-ambery smell, has remained a mystery until today. Herein, we prove by an eleven-step chemical synthesis, employing a novel asymmetric organocatalytic Mukaiyama-Michael addition, that (+)-2-epi-ziza-6(13)en-3-one is the active smelling principle of vetiver oil. Its olfactory evaluation reveals a remarkable odor threshold of 29 picograms per liter air, responsible for the special sensuous aura it lends to perfumes and the quasi-pheromone-like effect it has on perfumers and consumers alike.

Conformational Investigations in Flexible Molecules Using Orientational NMR Constraints in Combination with 3J-Couplings and NOE Distances.

The downscaling of NMR tensorial interactions, such as dipolar couplings, from tens of kilohertz to a few hertz in low-order media is the result of dynamics spanning several orders of magnitudes, including vibrational modes (~ns-fs), whole-molecule reorientation (~ns) and higher barrier internal conformational exchange (

Gold Difluorocarbenoid Complexes: Spectroscopic and Chemical Profiling.

Gold carbenes of the general type [LAu=CR2 ]+ are sufficiently long-lived for spectroscopic inspection only if the substituents compensate for the largely missing stabilization of the carbene center by the [LAu]+ fragment. π-Donation by two fluorine substituents (R=F) is insufficient; rather, difluorocarbene complexes are so deprived in electron density that they sequester even "weakly coordinating" anions such as triflate or triflimide. This particular bonding situation translates into unmistakable carbenium ion chemistry upon reaction with stilbene as a model substrate.

A multi-substrate screening approach for the identification of a broadly applicable Diels-Alder catalyst.

When developing a synthetic methodology, chemists generally optimize a single substrate and then explore the substrate scope of their method. This approach has led to innumerable and widely-used chemical reactions. However, it frequently provides methods that only work on model substrate-like compounds. Perhaps worse, reaction conditions that would enable the conversion of other substrates may be missed. We now show that a different approach, originally proposed by Kagan, in which a collection of structurally distinct substrates are evaluated in a single reaction vessel, can not only provide information on the substrate scope at a much earlier stage in methodology development, but even lead to a broadly applicable synthetic methodology. Using this multi-substrate screening approach, we have identified an efficient and stereoselective imidodiphosphorimidate organocatalyst for scalable Diels-Alder reactions of cyclopentadiene with different classes of α,ß-unsaturated aldehydes.

A Purely Organic Tricarbanion.

How many carbanions can an organic molecule accommodate? The formation of purely organic carbanions with multiple charges is challenging as charge stabilization cannot be achieved through metal coordination. Previously, only quaternary ammonium dicarbanion salts had been reported. By using highly electron-deficient trifluoromethanesulfonyl (triflyl or Tf) groups, the formation of a purely organic tricarbanion has been realized for the first time.

The Catalytic Asymmetric Mukaiyama-Michael Reaction of Silyl Ketene Acetals with α,ß-Unsaturated Methyl Esters.

α,ß-Unsaturated esters are readily available but challenging substrates to activate in asymmetric catalysis. We now describe an efficient, general, and highly enantioselective Mukaiyama-Michael reaction of silyl ketene acetals with α,ß-unsaturated methyl esters that is catalyzed by a silylium imidodiphosphorimidate (IDPi) Lewis acid.

1,1,3,3-Tetratriflylpropene (TTP): A Strong, Allylic C-H Acid for Brønsted and Lewis Acid Catalysis.

Tetratrifylpropene (TTP) has been developed as a highly acidic, allylic C-H acid for Brønsted and Lewis acid catalysis. It can readily be obtained in two steps and consistently shows exceptional catalytic activities for Mukaiyama aldol, Hosomi-Sakurai, and Friedel-Crafts acylation reactions. X-ray analyses of TTP and its salts confirm its designed, allylic structure, in which the negative charge is delocalized over four triflyl groups. NMR experiments, acidity measurements, and theoretical investigations provide further insights to rationalize the remarkable reactivity of TTP.