A Heteroleptic Dirhodium Catalyst for Asymmetric Cyclopropanation with α‐Stannyl α‐Diazoacetate. “Stereoretentive” Stille Coupling with Formation of Chiral Quarternary Carbon Centers

Chiral Bismuth-Rhodium Paddlewheel Complexes Empowered by London Dispersion: The C-H Functionalization Nexus

Heterobimetallic [BiRh] tetracarboxylate catalysts endowed with 1,3-disilylated phenylglycine paddlewheels benefit from interligand London dispersion. They were originally designed for asymmetric cyclopropanation but are now shown to perform very well in asymmetric C-H functionalization reactions too. Because of the confined ligand sphere about the derived donor/acceptor carbenes, insertions into unhindered methyl groups are kinetically favored, although methylene units also react with excellent levels of asymmetric induction; even gaseous ethane is a suitable substrate. Moreover, many functional groups in both partners are tolerated. The resulting products are synthetically equivalent to the outcome of traditional asymmetric ester alkylation, allylation, benzylation, propargylation and aldol reactions and therefore constitute a valuable nexus to more conventional chemical logic.

Highly Regio-, Stereo-, and Enantioselective Copper-Catalyzed B-H Bond Insertion of α-Silylcarbenes: Efficient Access to Chiral Allylic gem-Silylboranes

Herein, we report the development of a method for highly regio-, stereo-, and enantioselective B-H bond insertion reactions of α-silylcarbenes generated from 1-silylcyclopropenes in the presence of a chiral copper(I)/bisoxazoline catalyst for the construction of chiral γ,γ-disubstituted allylic gem-silylboranes, which cannot be prepared by any other known methods. This reaction is the first highly enantioselective carbene insertion reaction of α-silylcarbenes ever to be reported. The method shows general applicability for various 3,3-disubstituted silylcyclopropenes and exclusively affords E-products. The novel chiral γ,γ-disubstituted allylic gem-silylborane products are versatile allylic bimetallic reagents with high stability and have great synthetic potential, especially for the construction of complex molecules with continuous chiral centers.

Diastereoselective Transfer of Tri(di)fluoroacetylsilanes-Derived Carbenes to Alkenes

Stereoselective cyclopropanation reaction of alkenes is usually achieved by metal complexes via singlet-metal-carbene intermediates. However, previous transition-metal-catalyzed cyclopropanation of alkenes with acylsilanes afforded low diastereoselectivity. Herein, we report the first visible-light-induced transition-metal-free cyclopropanation reaction of terminal alkenes with trifluoroacetylsilanes and difluoroacetylsilanes. Both aromatic and aliphatic alkenes as well as electron-deficient alkenes are suitable substrates for the highly cis-selective [2+1] cyclization reaction. A combination of experimental and computational studies identified triplet carbenes as being key intermediates in this transformation. The gram scale reaction and late-stage functionalization demonstrated the synthetic potential of this strategy.