Palladium-Catalyzed Cyclocarbonylative Synthesis of Dibenzoxazepinones

Significance

In 2005, Alper reported that palladium-complexed dendrimers supported on silica were efficient catalysts for the reaction shown above (S. M. Lu, H. Alper J. Am. Chem. Soc. 2005, 127, 14776). The current paper describes studies on the expansion of this work to in situ generated instead of a pre-complexed catalyst system. A bulky phosphaadamantane (Cytop 292) proved to be a very efficient ligand for this ­reaction. After some optimization, it was possible to go down to 15 psi CO pressure and 2% of catalyst loading with no erosion in yield. The yields were almost quantitative in every example, and functional groups, such as ester and nitrile, were tolerated in the reaction. Unfortunately, the substrate scope was quite poorly studied, for example, the tolerance towards other halogens would have been useful, as well as the use of heterocyclic biaryls. This level of study was carried out in the previous work (reference above), where the above-mentioned substrates afforded nearly quantitative yields of products. It is reasonable to expect similar performance from the current system.