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Abstract
The construction of chiral biaryl alcohols using enantio-relay catalysis is a particularly attractive synthetic method in organic synthesis. However, overcoming the intrinsic incompatibility of distinct organometallic complexes and the reaction conditions used are significant challenges in asymmetric catalysis. To overcome these barriers, we have taken advantage of an enantio-relay catalysis strategy and a combined dual-immobilization approach. We report the use of an imidazolium-based organopalladium-functionalized organic–inorganic hybrid silica and ethylene-coated chiral organoruthenium-functionalized magnetic nanoparticles to catalyze a cascade Suzuki cross-coupling–asymmetric transfer hydrogenation reaction to prepare chiral biaryl alcohols in a two-step, one-pot process. As expected, the site-isolated active species, salient imidazolium phase-transfer character and high ethylene-coated hydrophobicity can synergistically boost the catalytic performance. Furthermore, enantio-relay catalysis has the potential to efficiently prepare a variety of chiral biaryl alcohols. Our synthetic strategy is a general method that shows the potential of developing enantio-relay catalysis towards environmentally benign and sustainable organic synthesis.
Highlights
Key Laboratory of Resource Chemistry of Ministry of Education, Shanghai Key Laboratory of Rare Earth Functional Materials, Shanghai Normal University, Shanghai 200234, P
We report the use of an imidazolium-based organopalladiumfunctionalized organic–inorganic hybrid silica and ethylene-coated chiral organoruthenium-functionalized magnetic nanoparticles to catalyze a cascade Suzuki cross-coupling–asymmetric transfer hydrogenation reaction to prepare chiral biaryl alcohols in a two-step, one-pot process
We report the development of an enantio-relay catalyzed cascade Suzuki cross-coupling–asymmetric transfer hydrogenation reaction to prepare chiral biaryl alcohols (Figure 1)
Summary
The characteristic carbon signal at d 5 172.5 ppm was assigned as the carbon atoms of the NHC-Pd group, whose chemical shift were very similar to those of the NHC-Pd complex[28] This result demonstrated that the well-defined single-site active species was retained during the preparation. In the case of the Suzuki cross-coupling reaction of 4-iodoacetophenone and phenylboronic acid[35], catalyst 1 exhibited an increased catalytic activity when compared to its homogeneous counterpart (2) (88% conversion see SI in Table S1), indicating the phase-transfer function of the imidazolium functionality. These results were even better than those obtained using a combination of catalyst 1 and the homogeneous AreneRuTsDPEN catalyst, which afforded a 155351 mixture of 4-phenylacetophenol (92% ee), 4-iodophenylethanol and 1-phenylethanol (Table 1, entry 1 in brackets) The scope of this one-pot enantio-relay catalyzed process was investigated using a series of substituted substrates.
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