RESUMEN

The influence of microwave and ultrasonic irradiation on the performance of ammonium-tagged Ru-based catalysts in olefin metathesis transformations in aqueous media was studied. Differences in the catalytic activity in correlation with the nature of the present counter ion and the size of the N-heterocyclic carbene (NHC) ligand were revealed. The presented methodology allows for preparation of a variety of polar and non-polar metathesis products under environmentally friendly conditions.

RESUMEN

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.

RESUMEN

A tube-in-tube reactor was successfully applied in homo- and heterogeneous olefin metathesis reactions under continuous flow mode. It was shown that the efficient removal of ethylene facilitated by connection of the reactor with a vacuum pump significantly improves the outcome of metathesis reactions. The beneficial aspects of this approach are most apparent in reactions performed at low concentration, such as macrocyclization reactions. The established system allows achievement of both improved yield and selectivity, and is ideal for industrial applications.

Asunto(s)

Alquenos/química , Química/instrumentación , Dimetilpolisiloxanos/química , Solventes/química , Vacio

RESUMEN

[reaction: see text]. Application of triethylene glycol with catalytic quantity of zinc chloride (ZnCl2/TEG) is described as a new and efficient reaction medium for a difficult Fischer synthesis, leading to sensitive indoles. Transformation of the 3-acetyl-1-methylthiocycloalka[c]pyridine phenylhydrazones and p-methoxyphenylhydrazones into the 2-(2-pyridyl)indoles and 5-methoxy-2-(2-pyridyl)indoles, which are the synthons in our total synthesis of the sempervirine-type alkaloids, is carried out under controlled microwave irradiation in dry zinc chloride solution (0.16 M) in TEG. This protocol produces indoles from acetophenone or cyclohexanone via their phenylhydrazones in excellent yields.