Rhodium‐Catalyzed Asymmetric Synthesis of Silicon‐Stereogenic Dibenzosiloles by Enantioselective [2+2+2] Cycloaddition

Abstract

A rhodium-catalyzed asymmetric synthesis of silicon-stereogenic dibenzosiloles has been developed through a [2+2+2] cycloaddition of silicon-containing prochiral triynes with internal alkynes. High yields and enantioselectivities have been achieved by employing an axially chiral monophosphine ligand, and the present catalysis is also applicable to the asymmetric synthesis of a germanium-stereogenic dibenzogermole. Preliminary studies on the optical properties of these compounds are also described.

Carbene‐Catalyzed Desymmetrization and Direct Construction of Arenes with All‐Carbon Quaternary Chiral Center

“…(Figure 1c-2). To the best of our knowledge,this is the first success of an organocatalyzed [15] intermolecular reaction that allows simultaneous arene formation and desymmetrization with remotechirality control. [16] It shall significantly simplify the synthesis of aryl-containing molecules with challenging chiral centers.…”

A Catalytic SEAr Approach to Dibenzosiloles Functionalized at Both Benzene Cores

“…[1][2][3] These members of the metallole family distinguish themselves from their all-carbon analogues in their unique electronic structure,and hence are valuable building blocks for p-conjugated conducting polymers.Elegant procedures for the catalytic synthesis of siloles fused to two benzene rings have been reported, including palladium-catalyzed CÀH/CÀOTf, [4] CÀI/SiÀH, [5] and SiÀMe/ C À Br coupling reactions, [6] as well as iridium-and rhodiumcatalyzed [2+ +2+ +2] cycloadditions of silicon-tethered diynes with alkynes. [7,8] Recently,r ing closures starting from orthosilylated biphenyls 1 to dibenzosiloles 2 were established. These approaches are particularly attractive because of the convenient availability of the starting materials,t hereby allowing rapid access to functionalized silole motifs.T hree conceptually different methods for this intramolecular formation of the C À Si bond were developed: [9] transition-metalcatalyzed C À H/Si À Hc oupling, [10] homolytic aromatic substitution involving silicon-centered radicals, [11,12] and electrophilic aromatic substitution (S E Ar) with stabilized silicon cations.…”

Rhodium‐Catalyzed Synthesis and Optical Properties of Silicon‐Bridged Arylpyridines

“…The exclusive formation of 7 aa in 92 % yield was achieved with somewhat higher, but still unsatisfactory enantioselectivity (40 % ee ( S )) through the use of ligand ( R )‐ L1 with a methyl group at the 3′‐position (entry 3). Ligand ( R )‐ L1 was previously employed by our group as an effective chiral ligand for the asymmetric synthesis of related silicon‐stereogenic dibenzosiloles and silicon‐bridged arylpyridinones . To further improve the enantioselectivity, we prepared a new chiral ligand with an isopropyl group at the 3′‐position (( R )‐ L2 ) and found that high overall enantioselectivity of 89 % ee ( S ) could be achieved at the cost of reactivity (39 % yield of 6 aa and 41 % yield of 7 aa ; entry 4).…”