An Interrupted Pummerer/Nickel‐Catalysed Cross‐Coupling Sequence

Abstract

An interrupted Pummerer/nickel‐catalysed cross‐coupling strategy has been developed and used in the elaboration of styrenes. The operationally simple method can be carried out as a one‐pot process, involves the direct formation of stable alkenyl sulfonium salt intermediates, utilises a commercially available sulfoxide, catalyst, and ligand, operates at ambient temperature, accommodates sp‐, sp2‐, and sp3‐hybridised organozinc coupling partners, and delivers functionalised styrene products in high yields over two steps. An interrupted Pummerer/cyclisation approach has also been used to access carbo‐ and heterocyclic alkenyl sulfonium salts for cross‐coupling.

Bond-Forming and -Breaking Reactions at Sulfur(IV): Sulfoxides, Sulfonium Salts, Sulfur Ylides, and Sulfinate Salts

“…Recently, the Procter group utilized the intermediary sulfonium salts that are obtained via interrupted Pummerer reactions as transient leaving groups for an in situ nickelcatalyzed Negishi-type cross coupling in a one-pot manner (Scheme 29, for more information on the cross coupling of sulfonium salts, see section 3.2). 85 A broad scope of organozinc reagents was employed, and the reaction could be expanded to aryl-and alkynylsulfonium salts as well as to domino C−C bond formation employing suitable tethers.…”

Radical C−C Bond Formation using Sulfonium Salts and Light

“…More recently, several groups have contributed to establishing intermolecular C−H sulfenylation using sulfoxides as a facile means for accessing sulfonium salts . Within these reports, sulfonium salts have proved effective electrophilic partners in transition metal‐catalysed C−C cross‐couplings . In particular, formal C−H cross‐couplings can occur when C−H sulfenylation and C−C bond formation are carried out in one pot …”

Synthesis of Pyridylsulfonium Salts and Their Application in the Formation of Functionalized Bipyridines

“…With respect to the mechanism, the coupling reaction is proposed to proceed through the formation of a sulfurane intermediate: attack of the organolithium species at the electropositive sulfur center, followed by subsequent ligand-coupling of the two pyridine units forms the bipyridine product and phenyltolylsulfide (Scheme ). Sulfuranes bearing solely carbon substituents have been proposed and detected previously. , Recently they have been invoked in aryl–aryl, aryl–vinyl, and vinyl–vinyl couplings. , In our case, the selectivity for bipyridine formation over pyridyl–aryl or phenyl–tolyl couplings can be rationalized as follows: the incoming nucleophile would be expected to occupy an apical position and ligand coupling with an equatorial pyridine would be favored over phenyl or tolyl groups. ,, The reaction pathway may involve pseudorotations if both pyridines occupy the apical positions in the initially formed intermediate.…”

“…Sulfonium salts have garnered considerable attention of late in organic synthesis, especially for their utility in mediating C–C bond formation (Scheme ). , Examples using sulfonium salts bearing sp 2 -hybridized carbon substituents include reactions of vinylsulfonium salts to generate pharmaceutically relevant heterocycles, cross-couplings, and transformations using the extremely versatile thianthrenium and benzothiophenium salts . Triarylsulfonium salts have been demonstrated to be particularly versatile reagents, capable of forming C–C bonds via various different methods. ,, …”