The synthesis of several natural products’ frameworks is carried out by means of a diastereoselective intramolecular Pauson–Khand reaction promoted by molecular sieves. Diastereoselectivity is achieved only if a coordinating group is present at a convenient distance from the alkene moiety. Naphthalenes can be obtained directly under refluxing toluene conditions.
experimental conditions have been developed for an efficient catalyticPauson–Khandreaction. These are based on the use of a mixture of molecular sieves and tert-butanol as inducers of the process. This mixture, with the appearance of a paste, is able to adsorb CO, thus improving the conversion and making it possible to effect the reactions in the absence of a CO atmosphere. The protocol is applied
Enynes, easily obtained by the Sonogashira coupling reactions of aromatic iodides. undergo. with good yields, en ne metathesis using the Grubbs catalyst. The resulting dienes are interesting carbo- and heterocycles which can give complex natural frameworks by Diels Alder reactions. Thus. an estradiol type skeleton is obtained in two steps from the corresponding enynes. An example of a metathesis-Diels-Alder cascade one-pot process is reported. (C) 2001 Elsevier Science Ltd. All rights reserved.