Rhodium‐Catalyzed Enantioselective Radical Addition of CX₄ Reagents to Olefins

Abstract

We describe an enantioselective addition of Br-CX3 (X = Cl or Br) to terminal olefins that introduces a trihalomethyl group and generates optically active secondary bromides. Computational and experimental evidence supports an asymmetric atom transfer radical addition (ATRA) mechanism in which the stereodetermining step involves outer-sphere bromine abstraction from a (bisphosphine)Rh(II)BrCl complex by a benzylic radical intermediate. Beyond the synthetic utility, this mechanism appears unprecedented in asymmetric catalysis.

Reaction Mechanism and Kinetics study on Addition of CCl4 to 1‐hexene Catalyzed by Mo‐Mo Quintuply‐bond

“…Also, carbon-halogen bond was occasionally cleaved by harsh UV light to initiate the catalytic reaction. [15,16] Subsequently, lots of metal-mediated catalysts, such as Cu, [17] Ni, [18,19] Ru, [20,21] Pd [22] and Fe [23] catalysts were used as radical initiators in ATRA process, showing a high reaction efficiency. In this regard, the metal can trigger generation of free radicals, while formed metal-halide complex can achieve rapid transfer of the halide from the metal to the carbon-centered radical.…”

Chlorotrifluoromethylation of Terminal Olefins by Atom Transfer‐Type Radical Reaction Catalyzed by Cobalt Complexes

“…Considering the result obtained with vitamin B 12 catalysis (Table , entry 12), the possibility of stereoselective chlorotrifluoromethylation was examined (Table ). Generally, dual functionalization of olefins by the atom transfer radical reaction have faced poor stereoselectivity because of the difficulty in controlling the reactivity around the catalytically active center . Indeed, when 1i was used as the substrate, both the Co III porphyrin and salen complexes resulted in low selectivity (entries 1–3).…”

Sulphide as a leaving group: highly stereoselective bromination of alkyl phenyl sulphides

“…Potentially very useful, but rare, asymmetric protocols for obtaining benzylic bromides are emerging. These include the recently reported Rh-catalysed asymmetric Kharasch addition to styrenes,25 and the Cu-catalysed formal asymmetric hydrobromination of styrenes 26. However, these methods require the use of precious metal-chiral phosphine catalysis and display limited substrate scope.…”