Enantioselective construction of six- and seven-membered triorgano-substituted silicon-stereogenic heterocycles

Abstract

The exploitation of chirality at silicon in asymmetric catalysis is one of the most intriguing and challenging tasks in synthetic chemistry. In particular, construction of enantioenriched mediem-sized silicon-stereogenic heterocycles is highly attractive, given the increasing demand for the synthesis of novel functional-materials-oriented silicon-bridged compounds. Here, we report a rhodium-catalyzed enantioselective construction of six- and seven-membered triorgano-substituted silicon-stereogenic heterocycles. This process undergoes a direct dehydrogenative C−H silylation, giving access to a wide range of triorgano-substituted silicon-stereogenic heterocycles in good to excellent yields and enantioselectivities, that significantly enlarge the chemical space of the silicon-centered chiral molecules. Further elaboration of the chiral monohydrosilane product delivers various corresponding tetraorgano-substituted silicon-stereogenic heterocycles without the loss of enantiopurity. These silicon-bridged heterocycles exhibit bright blue fluorescence, which would have potential application prospects in organic optoelectronic materials.

Enantioselective C–H Functionalization toward Silicon-Stereogenic Silanes

“…Moreover, when using a different structure of Josiphos-type ligand L4, several seven-membered carbazole-based siliconstereogenic heterocycles bearing different substituents were also obtained in good yields and enantioselectivities (Scheme 15). 22 Methoxy (70a), OBn (70b), OTs (70c), fluoro (70d), and thiophenyl (70e) functional groups were all well tolerated in the transformation. Treatment of the seven-membered siliconstereogenic monohydrosilane 70a with vinyl ferrocene produces the oxidative alkenylation product 71 in 50% yield without the loss of enantiopurity.…”

“…In 2021, our group developed a novel rhodium-catalyzed enantioselective dehydrogenative C–H silylation for the construction of six- and seven-membered triorgano-substituted silicon-stereogenic heterocycles (Schemes 14 and 15). 22 A wide range of functionalized six-membered heterocycles bearing silicon stereocenters was efficiently constructed, with the products being obtained in good yields and excellent enantioselectivities (up to >98% ee ) (Scheme 14 ). Indole ( 68a – c ), benzothiophene ( 68d ), benzofuran ( 68e ), and silicon-bridged diphenylamine ( 68f ) skeletons were all compatible in this transformation, delivering the corresponding six-membered silicon-stereogenic heterocycles with high efficiency.…”

Recent Progress in Transition Metal‐Catalyzed Hydrosilane‐Mediated C−H Silylation

“…According to the similar strategy, He group successfully synthesized a series of six-and seven-membered chiral monohydrosilanes via Rh-catalyzed intramolecular C(sp 2 )À H asymmetric silylation on heterocyclic skeletons (Scheme 29(a)). [46] In the system, substrates played an important role in getting the stable chiral monohydrosilanes. Besides, the reaction likely through seven-membered and eight-membered metalacyclic states.…”

Construction of Si‐Stereogenic Silanes through C−H Activation Approach

“…The group of C. He applied the approach of Rh‐catalyzed asymmetric dehydrogenative silylation to construct the six‐ and seven membered cyclic monohydrosilanes bearing a chiral silicon center (Scheme 10). [22] Preliminary photophysical properties investigations unveiled the promising potential as the optoelectronic material of this class of π‐conjugated enantioenriched monohydrosilanes due to their bright blue fluorescence under UV light irradiation.…”