[GRAPHICS]The Pauson-Khand reaction still has a relatively low scope with respect to the used carbon skeleton, while yields are low in many other cases. We have observed that the addition of molecular sieves improves yields remarkably, Experimental protocol is extremely easy, and it has been applied to several substrates including the less favorable ones.
Aromatic enynes as substrates for the intramolecular Pauson-Khand reaction
Pauson-Khand reactions are carried out with different substituted aromatic enynes yielding tricyclic cyclopentenones related to natural products. Reaction is promoted by dissolved Me3NO. Isomerization of the double bond of the cyclopentenone is observed except for compound 2e, with a non terminal triple bond.
Pauson-Khandreactions are carried out with different substituted aromatic enynes, yielding tricyclic cyclopentenones related to natural products such as chromenes. Enynes are easily obtained in a two-step approximation from the corresponding salicylaldehydes. The reaction is promoted by dissolved TMANO (trimethylamine N-oxide) and/or 4 A molecular sieves. This new way of induction for the Pauson-Khand