Carbon-silicon-switch effect in enantioselective construction of silicon-stereogenic center from silacyclohexadienones
Yu Yan, Qi Wei, Zhishan Su, Nan‐Nan Hang, Tamio Hayashi, Jialin Ming
Abstract
Carbon-silicon-switch strategy, replacing one specific carbon atom in organic molecules with a silicon, has garnered significant interest for developing new functional molecules. However, the influence of a reaction regarding its selectivity and reactivity by carbon-silicon-switch strategy has far less been investigated. Here we discover an unusual carbon-silicon-switch effect in the enantioselective construction of silicon-stereogenic center. It is found that there has been a significant change in the desymmetrization reaction of silacyclohexadienones using asymmetric conjugate addition or oxidative Heck reaction with aryl/alkyl nucleophiles when compared with their carbon analogues cyclohexadienones. Specifically, the carbon-silicon-switch leads to a reversal in enantioselectivity with arylzinc as the nucleophile by the same chiral catalyst, and results in totally different reactivity with arylboronic acid as the nucleophile. Control experiments and density functional theory (DFT) calculations have shown that the unusual carbon-silicon-switch effect comes from the unique stereoelectronic feature of silicon. Silicon has been incorporated into organic molecules in place of carbon under the principle that, given that they belong to the same periodic group, their reactivity could be similar. Here, the authors perform desymmetrizations on silacyclohexenone and the carbon analogue, with the two substrates yielding opposite enantiomers, showing that our understanding of the similarities of the two atoms is incomplete.