Copper‐Catalyzed Asymmetric Three‐Component Borylstannation: Enantioselective Formation of CSn Bond

Abstract

In summary, a first copper-catalyzed synthesis of a-aryl-b-borylstannane compounds was accomplished through three-component borylstannation of aryl-substituted alkenes. In the exploration of an asymmetric variant, chiral sulfinylphosphine ligands proved advantageous in controlling stereochemistry of BÀCu addition and in promoting transmetalation of enantioenriched alkylÀCu species. The stereochemical outcome supported a sequential syn-borylcupration and configuration-retentive transmetalation mechanism. Moreover, a-chiral b-borylstannanes were easily transformed into a diverse array of secondary alkylstannanes and triarylethane with high enantiomeric purity. The applications of chiral sulfinylphosphine ligands to other tandem CuÀB addition reactions are currently under investigation in our group.Configurationally stable nonracemic organometallic compounds (organoboron, organosilane, and organotin) [1] are emerging as a class of important chiral reagents. Their carbonmetal bonds can be readily transformed to stereogenic carbon-carbon [2] and carbon-heteroatom bonds, [3] providing novel and concise routes to syntheses of natural products and chiral drugs. Among these organometallic compounds, secondary alkylstannanes are configurationally robust and easily stored, and have been utilized in many asymmetric transformations, such as Stille-type cross-coupling reactions, [4] allylstannations, [5] and transmetalations to other organometallic species.[6]Conventional methods to reach optically active organostannanes include chiral resolution, [4f] substrate control, [4c, 7] and reagent induction, [8] whereas asymmetric catalysis has been rather less thoroughly investigated. To date, only two cases relating to chiral secondary cyclic alkylstannane synthesis have been reported. In 2004, Gevorgyan and co-workers developed a Rh I -catalyzed enantioselective hydrostannation of cyclopropene to generate cyclopropylstannanes.[9a] More recently, Studer and co-workers [9b] reported a Cu I -catalyzed asymmetric annulation of 2-nitrosopyridine and allylstannane to furnish tin-substituted isoxazolidines (Scheme 1 a,b). However, to our knowledge, a general and versatile catalytic asymmetric method for the construction of acyclic alkylstannanes remains unreported.[10] Herein we present a new Cu-catalyzed asymmetric dimetalation (three-component reaction) strategy to access to enantiomerically enriched organostannanes (Scheme 1 c).Bis-metalated alkene moieties are of increasing importance in the preparation of medical reagents and complex molecules through cascade transformations. [2g, 11a] Asymmetric catalytic approaches to dimetalation have relied primarily on noble metal (Pt, Rh, and Pd) catalysis.[11] Very recently, Hoveyda and co-workers disclosed a copper-catalyzed double borylcupration to alkynes that afforded 1,2-diboronated alkanes in high enantioselectivities.[12] Borylcupration has also been widely employed as an elegant strategy for enantioselective hydro/difunctionalization of alkenes, [13] including hydro...

Transition‐Metal‐Catalyzed Three‐Component Difunctionalizations of Alkenes

“…The asymmetric borylstannation of alkenes was also accomplished by using a copper/chiral sulfinylphosphine catalyst . This reaction used B 2 (pin) 2 as a borating reagent and R 3 SnOMe as a tin source and led to the production of various α‐aryl‐β‐borylstannane compounds in good‐to‐high yields with high ee .…”

Green Copper Catalysis in Enantioselective Domino Reactions

“…R 1 = 1-Na p h, R 2 = Ph: 94%, 96% de, 94% ee R 1 = o-Tol , R 2 = Ph: 83%, 84% de, 94% ee R 1 = p -MeOC 6 H 4, R 2 = Ph: 70%, 80% de, 88% ee R 1 = p -FC 6 H 4, R 2 = Ph: 87%, 84% de, 88% ee R 1 = ( E ) -PhCH=CH , R 2 = Ph: 66%, 92% de, 92% ee R 1 = ( E ) -PhCH=C ( Me ), R 2 = Ph: 86%, 88% de, 86% ee R 1 = CH 2 Bn, R 2 = Ph: 80%, 96% de, 85% ee R 1 = Ph, R 2 = p -MeOC 6 H 4 : 69%, 90% de, 96% ee R 1 = Ph, R 2 = p -F 3 CC 6 H 4 : 79%, 80% de, 84% ee R 1 = Ph, R 2 = 2-thien y l: 73%, 94% de, 92% ee R 1 = Ph, R 2 = SiEt 3 : 83%, 88% de, 70% ee In 2015, asymmetric copper-catalyzed borylstannations of aromatic alkenes 136, B 2 (Pin) 2 and Bu 3 SnOMe were developed by Liao et al, as shown in Scheme 48 [59]. Using a chiral catalyst in situ generated from CuCl and chiral sulfinylphosphine ligand 137, the three-component reaction afforded the corresponding chiral α-arylβ-borylstannanes 138 in moderate to quantitative yields (63-99%) and good to high enantioselectivities (86-96% ee).…”

Recent Developments in Enantioselective Metal‐Catalyzed Domino Reactions

“…Other functionalizations of alkenes, such as asymmetric borylstannations, have been very recently described by Liao et al 126. This study dealt with an enantioselective copper‐catalyzed three‐component reaction between styrenes 295a–n , B 2 (pin) 2 and Bu 3 SnOMe performed at 20 °C in the presence of chiral sulfinylphosphine ligand 296 and CuCl as precatalyst in THF as solvent (Scheme ).…”