Cristina Nieto-Oberhuber

Enantioselective Synthesis of (+)-Cortistatin A, a Potent and Selective Inhibitor of Endothelial Cell Proliferation

This manuscript describes an enantioselective synthesis of the naturally occurring inhibitor of endothelial cell proliferation, cortistatin A. Key steps of the synthesis are a silicate-directed elimination/ring expansion reaction and a highly diastereoselective aza-Prins cyclization with a subsequent transannular etherification.

Metal cyclopropyl carbenes in the reactions of alkynes with alkenes and furans

Electrophilic transition-metal complexes catalyze the reaction of enynes in the presence of water or alcohols to give hydroxy- or alkoxycyclization derivatives. The reaction proceeds by the anti addition of the alkene and the metal to the alkyne. The key intermediates in this reaction are cyclopropyl metal carbenes, which are also probably involved in the metathesis-type rearrangement of enynes. A general scheme is proposed for the cyclization of enynes initiated by the coordination of the metal to the enyne by transition metals, which included 5-exo -dig and 6-endo -dig pathways. The intramolecular reaction of furans with alkynes also proceeds via cyclopropyl metal carbenes.

INTRAMOLECULAR REACTIONS OF ALKYNES WITH ALKENES CATALYZED BY PLATINUM AND GOLD

Two major pathways are followed in the reaction of alkenes with alkynes catalyzed by electrophilic transition metals. If the metal coordinates the alkyne and the alkene, an oxidative cyclometallation can ensue to give a metallacyclopentene, which usually evolves by β-hydrogen elimination (Alder-ene cycloisomerization). Alternatively, the selective coordination of the metal to the alkyne promotes an attack of the alkene (usually anti) to give cyclopropyl metal carbenes.