The well‐known Corey–Bakshi–Shibata (CBS) reduction is a powerful method for the asymmetric synthesis of alcohols from prochiral ketones, often featuring high yields and excellent selectivities. While steric repulsion has been regarded as the key director of the observed high enantioselectivity for many years, we show that London dispersion (LD) interactions are at least as important for enantiodiscrimination. We exemplify this through a combination of detailed computational and experimental studies for a series of modified CBS catalysts equipped with dispersion energy donors (DEDs) in the catalysts and the substrates. Our results demonstrate that attractive LD interactions between the catalyst and the substrate, rather than steric repulsion, determine the selectivity. As a key outcome of our study, we were able to improve the catalyst design for some challenging CBS reductions.
Recently, the Furstner group reported the first general trans-hydroboration of internal alkynes by using a cationic ruthenium(II) complex, [Cp*Ru(MeCN) 3 ]PF 6 , as the catalyst. Density functional theory (DFT) calculations have been carried out to elucidate the reaction mechanism and the origin of stereoselectivity. The reaction mechanism was suggested to initiate with the rate-determining oxidative hydrogen migration to stereoselectively form a metallacyclopropene intermediate (that determines the trans selectivity), followed by a reductive boryl migration to form the unusual trans-addition alkenyl-borane product. A combined ion-mobility mass spectrometry (IM-MS) and DFT study has also been employed to investigate the unsuccessful reaction with terminal alkynes. Key oxidative-coupling intermediates have been identified. Our results suggest that [2 + 2 + 2] cycloaddition of terminal alkynes to form a very stable arene compound could be the reason for the unsuccessful hydroboration of the terminal alkynes. Moreover, unreactive catecholborane reagent attributes the strong coordination of its arene part with the catalyst. Our proposed nonclassical mechanism also accounted for the other related Ru(II)-catalyzed reactions (such as hydrogenation and hydrogermylation). Our combined computational and experimental study provides in-depth mechanistic understanding and insights on the unusual trans-addition catalyzed by the cationic ruthenium(II) complexes and could help design the other trans-addition reactions.
Organosulfides have great significance and value in synthetic and biological chemistry. To establish a versatile and green methodology for C-S bond generation, we successfully developed a new aerobic cross-dehydrogenative coupling of C-H and S-H to synthesize aryl sulfides in water, utilizing CoPcS as the catalyst and O as the oxidant. This protocol shows great tolerance of a wide range of substrates. A large variety of organosulfur compounds were produced in modest to excellent yields.
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