A resourceful new strategy in organic synthesis: Tandem and stepwise metathesis/non-metathesis catalytic processes

Unconventional Reactivity of a Grubbs Catalyst: Hydroalkylation Overriding Metathesis

Unprecedented reactivity of a Grubbs catalyst has been disclosed in a reaction between vinyl azaarenes and alkenylnitriles under standard metathesis conditions. No metathesis was observed; only hydroalkylation products were obtained in high yields. The practical utility of this method has been demonstrated by the application of the products in useful transformations, e.g., the formation of cyclic iminoesters and highly challenging medium-sized carbocycles.

Dual Activity of Grubbs-Type Catalyst in the Transvinylation of Carboxylic Acids and Ring-Closing Metathesis Reactions

The development of a multifunctional catalyst, which mimics the promiscuity of enzymes, that would catalyze more than one chemical transformation in a single reaction vessel is one of the key points of modern sustainable chemistry. The results of our experiments indicated that Grubbs-type catalysts possess such multitask activity, catalyzing the transvinylation reaction of carboxylic acids without losing their original metathetic activity. This new activity of Grubbs catalysts was evidenced on several examples. It allows us to design a transvinylation/ring-closing metathesis (RCM) cascade reaction leading to the formation of endocyclic enol lactones from unsaturated carboxylic acids in an one-pot procedure. This unique ability of Grubbs catalyst to catalyze multiple mechanically distinct cascade reactions in a chemoselective way offers the new possibility for the synthesis of complex compounds from simple, easily accessible substrates.

A Light-Activated Olefin Metathesis Catalyst Equipped with a Chromatic Orthogonal Self-Destruct Function

A sulfur-chelated photolatent ruthenium olefin metathesis catalyst has been equipped with supersilyl protecting groups on the N-heterocyclic carbene ligand. The silyl groups function as an irreversible chromatic kill switch, thus decomposing the catalyst when it is irradiated with 254 nm UV light. Therefore, different types of olefin metathesis reactions may be started by irradiation with 350 nm UV light and prevented by irradiation with shorter wavelengths. The possibility to induce and impede catalysis just by using light of different frequencies opens the pathway for stereolithographic applications and novel light-guided chemical sequences.

Effective immobilisation of a metathesis catalyst bearing an ammonium-tagged NHC ligand on various solid supports

An ammonium-tagged ruthenium complex, 8, was deposited on several widely available commercial solid materials such as silica gel, alumina, cotton, filter paper, iron powder or palladium on carbon. The resulting catalysts were tested in toluene or ethyl acetate, and found to afford metathesis products in high yield and with extremely low ruthenium contamination. Depending on the support used, immobilised catalyst 8 shows also additional traits, such as the possibility of being magnetically separated or the use for metathesis and subsequent reduction of the obtained double bond in one pot.

FT Raman--a valuable tool for surveying kinetics in RCM of functionalized dienes

In this article the suitability of FT Raman spectroscopy for monitoring kinetics of ring-closing metathesis promoted by the Grubbs' 1st generation precatalyst was demonstrated for the first time. Reactions at room temperature and under low catalyst loadings were carried out on a series of representative diene substrates. The time evolution of the characteristic Raman stretching vibrations unequivocally described the reaction progress allowing for precise calculation of the substrate conversion and of the yield in the expected cyclic product, based on the corresponding peak heights. The responsive Raman technique demonstrated clean RCM pathways for diethyl diallylmalonate and diallyl ether whereas a minor olefinic side-product was detected in the case of diallyl phthalate. The study provides essential underpinnings for future utilization of Raman spectroscopy, concurrently with NMR or supplementing it, for the evaluation of RCM reactions.

Ruthenium-catalyzed tandem enyne metathesis/hydrovinylation

In situ modification of Grubbs' first-generation metathesis catalyst allows for a tandem enyne metathesis/hydrovinylation that is complementary to the regioselectivity of known ruthenium-catalyzed hydrovinylations.