Cross metathesis of conjugated enynes

Abstract

1. Cross Metathesis of Conjugated Enynes : The Causes for High Z-Selectivity Cross-metathesis of a range of conjugated enynes with alkenes turns out to proceed with preferential formation of (Z)-isomers over (E)-isomers up to >25:1, which is unusual for cross-metathesis by Ruthenium catalyst. The kinetic study on formation of product and the Z/E ration with respect to time shows that catalysis doesn``t alter the Z/E ratio from the beginning of the experiment and the products form within 30 minutes of the catalyst addition, the implying that the reaction is under the kinetic control. The driving forces for this are attributed to steric hindrance between substituents and NHC ligand in the putative metallacyclobutane as well as chelation effects of suitably positioned functional groups to Ru, which is strongly supported by ab initio calculations. 2. Lactonization of Aromatic Carboxylic Acid Derivatives via C-H Activation An one-step synthesis of phthalide derivatives has been achieved from aromatic carboxylic acid via carbon-hydrogen bond activation. In this study, two different transition metal catalyst systems were used: Shilov and Palladium/oxidant/base Systems. Whereas Shilov system requires higher temperature, the substrate scope is wider than palladium system. Palladium/oxidant/base system can carry out the lactonization of the benzoic acid at lower temperature but suffers seriously from decarboxylation. Both systems result in phthalide derivatives from aromatic benzoic acid with moderate yield.