Alternatives to Organoboron Reagents in Rhodium‐Catalyzed Conjugate Additions

Abstract

The rhodium-catalyzed conjugate addition of organoboron reagents to alkene acceptors has emerged as an important methodology in organic synthesis. The process results in the formation of new carbon-carbon bonds, and in principle, can create new stereocenters at both the alpha and beta carbon atoms of the acceptor. Other organometallics are known to participate in the key transmetalation to rhodium and are becoming more established in stereoselective synthesis (notably arylzinc reagents). This Focus Review will describe recent developments in the use of alternative organometallic donors to organoboron reagents in rhodium-catalyzed conjugate addition reactions and their growing applications in synthesis.

Uncatalyzed conjugate addition of organozinc halides to enones in DME: a combined experimental/computational study on the role of the solvent and the reaction mechanism

“…[2][3][4][5] Two kinds of organometallic species can add to electron poor alkenes: those having high intrinsic nucleophilicity and so character, such as organocopper reagents, 6 and those having low intrinsic nucleophilicity but aptitude to transmetallate easily to transition-metal complexes, such as organoboronic acids 7,8 or organozinc reagents. 9,10 The rst ones are obtained by transmetallation starting from other organometallic precursors, such as Grignard or organolithium reagents or organozinc halides. 11 The others require the use of a transition metal catalyst to be converted into a nucleophilic organometallic species.…”

Trans-Selective Rhodium Catalysed Conjugate Addition of Organoboron Reagents to Dihydropyranones

“…The rhodium-catalysed conjugate addition of organometallic donors has evolved into a versatile tool for the assembly of complex molecules and intermediates in natural product synthesis [ 1 , 2 , 3 , 4 , 5 , 6 ]. The mechanistic and stereochemical aspects of the reaction have been thoroughly investigated for additions to prochiral substrates [ 7 ] and processes involving enantioselective protonation [ 8 , 9 , 10 ].…”

Exploring Rhodium-Catalysed Conjugate Addition of Chiral Alkenylboronates Using Chiral Olefin Ligands

“…Despite the considerable advances in catalyst design and substrate (acceptor) diversity, the structure of the organometallic donor remains surprisingly limited to aryl (and a number of alkenyl) derivatives. 7 Although there are a number of useful methods available for the preparation of complex enantiopure organoboron derivatives, only isolated examples of conjugate addition reactions have been reported. 8 In a notable example, the synthesis of hermitamides A and B (natural products isolated from the marine cyanobacterium Lyngbya majuscula) have been completed using rhodium-catalysed addition of an enantiopure alkenylboron reagent to an acrylamide.…”