Development of intermolecular additive free Pauson-Khand reactions for estrone E-ring extension using microwaves

Intermolecular additive free microwave (MW) promoted and cobalt octacarbonyl mediated Pauson-Khand reaction (PKR) performance was improved for estrone ring extension. The reaction development with norbornene and cyclopentene produced cyclopentenones in yields of comparable levels with those previously obtained with the aid of chemical additives as promoters. The PKRs with norbornene demonstrated that a low cobalt complex concentration increases yields, especially for the aliphatic alkynes. Furthermore, a boost for the MW PKR could be obtained by a gradual cobalt complex addition. These expedients combined with the use of an excess of free and cobalt complexed alkyne led to successful estrone ring system extension with various alkynes. (C) 2008 Elsevier Ltd. All rights reserved.