In recent years, the use of gallium compounds has made it possible to significantly enrich the chemistry of donor-acceptor cyclopropanes and their analogs, such as styrylmalonates and donor-acceptor alkenes. There are almost no alternatives to gallium compounds as a Lewis acid for carrying out a wide range of effective reactions involving these substrates. However, these transformations in most cases require the addition of equimolar amounts of gallium halides, which is associated with a number of difficulties including the low enantioselectivity of the reactions as well as the need to use special equipment due to the high hydrolytic instability of GaHal3.
In the context of ongoing research by the scientists of laboratory № 6 of ZIOC RAS on gallium-catalyzed organic transformations, fundamentally new catalysts based on cationic gallium phthalocyanines with weakly coordinating anions SbF6– and Sb2F11– have been developed. The synthesized catalysts showed high efficiency in the catalytic variant of cycloaddition/annulation of styryl malonates with aromatic aldehydes and styrene. The structural features of the obtained gallium catalysts as well as the details of the mechanism of the discovered process were thoroughly studied using 71Ga, 19F, and 121Sb NMR spectroscopy. This study is the first step towards the development of highly efficient transformations of donor-acceptor cyclopropanes under the action of catalytic amounts of gallium compounds.
R. A. Novikov, A. A. Levina, D. D. Borisov, A. D. Volodin, A. A. Korlyukov, Ya. V. Tkachev, Ya. B. Platonova, L. G. Tomilova, Yu. V. Tomilov Synthesis of the Cationic Gallium Phthalocyanines and Their Catalytic Application in Gallium(III)-Activated Processes for Donor−Acceptor Substrates Organometallics, 2020, 39, 2580–2593, DOI: 10.1021/acs.organomet.0c00113.