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Enantioselective Suzuki Cross-coupling Catalyzed by Non-metallocenic Planar Chiral Imine Palladacycleтезисы доклада
- Авторы: Dunina V.V., Gorunova O., Grishin Yu, Livantsov M., Ilyin M., Kochetkov K., Kuz’mina L., Churakov A.
- Сборник: Book of abstracts, Bit’c 3rd Annual Congress of Catalytic Asymmetric Synthesis (WCCAS-2012)
- Тезисы
- Год издания: 2012
- Место издания: Beijing, China
- Первая страница: 97
- Последняя страница: 97
- Аннотация: Unique activity of cyclopalladated compounds (CPC's) in achiral homogeneous catalysis has stimulated use of their chiral representatives as enantioselective catalysts. However, by contrast with impressive achievements in CPC-catalysed asymmetric Overman's rearrangements, cross-coupling catalysis by chiral palladacycles is poorly developed, with numerous reported failures in this field. Our research is devoted to development of an enantioselective Suzuki cross-coupling reaction catalyzed by palladacycles. First of all, we have found that only the CN-palladacycles offer an opportunity to perform Suzuki cross-coupling under extremely mild conditions. Thus, model reaction of para-tolyl bromide with phenyl boronic acid may be conducted at –18 oC, if cyclopalladated N,N-dimethylaminomethylferrocene is used as catalyst. Further we have performed screening a broad set of chiral CPC's in the reaction of 2-methoxynaphthyl-1 iodide with naphthyl-1 boronic acid affording atropoisomeric 1,1'-binaphthyl 2, with main attention focused on the catalysts of planar chirality. As the result, we have shown that maximum enantioselectivity (up to 53% ee) may be achieved using non-metallocenic cyclopalladated imine dimer (Spl)-1a as catalyst at low temperature. To note, this optical yield exceeds the known values of 26-40 %ee obtained previously for the same reaction with pincer CPCs. The optimal optical yield was obtained in toluene in air, the reaction occurs without any indications on the palladium black formation, and cyclopalladated catalyst was recovered in nearly quantitative yield (96 %) in the form of its myu-iodide analogue (Spl)-1b (X = I). The structure of the latter was unambiguously confirmed by spectral and X-ray diffraction study of its PPh3 derivative. Important conclusion may be derived from comparison of the reactions performed in aprotic medium and in alcohol. The reaction conducted in methanol affords binaphthyl product (Sa)-2 in more high yield (93 %) compared to that found in toluene, but it is attended with intensive deposition of palladium black, and results in decreased to 15% ee enantioselectivity. Such difference may be considered as an indirect evidence in support of the operation of two kinds of catalytic cycle, with dominant PdII/PdIV pathway in the aprotic solvent, while in alcohol classical PdII/Pd0 catalytic cycle becomes to be prevailing one.
- Добавил в систему: Дунина Валерия Владимировна