Si-O-Si Replacement of Spirobiindane Carbon Centers Unlocks a General Route to Tunable Chiral Spiro Ligands

The practical application of 1,1'-spirobiindane chiral ligands is often hindered by their lengthy preparation, especially for those ligands prepared from spirocyclic bisbenzylhalides. To streamline this process, we designed axially chiral spirocyclic architectures (SiOSPs) with three C(sp³)-atoms bridged by a Si-O-Si unit. We developed a Rh-catalyzed enantioselective dual C-H silylation of diarylsilanediol-derived disilyl ethers for the asymmetric construction of these structures. The resulting spirocyclic bisbenzyl bromides were efficiently synthesized via radical halogenation of 7,7'-dimethyl-SiOSPs, facilitating the concise preparation of various chiral spiro ligands and catalysts, demonstrated by the efficient synthesis of chiral spiro phospholane ligand (SITCP) analogues. This methodology enhances the structural tunability and diversity of silicon-integrated spiro-monophosphine ligands compared to carbon-based counterparts, opening new avenues for asymmetric catalysis. Notably, we achieved the enantioselective C-H bond functionalization of 2-naphthols with 1,3-dienes using the chiral SiOSP-derived C₁-symmetric monophosphine ligand 7e. Additionally, we synthesized spirocyclic diphenols (SiOSPOLs) from SiOSPs, which were refined to phosphoramidite ligands matching or exceeding SIPHOS's catalytic performance. Overall, this work streamlines the synthesis and enhances the structural modulation of chiral spirocyclic ligands and catalysts, while providing a novel class of spirocyclic bisphenol frameworks for asymmetric catalysis.