Tandem Ullmann–Goldberg Cross-Coupling/Cyclopalladation-Reductive Elimination Reactions and Related Sequences Leading to Polyfunctionalized Benzofurans, Indoles, and Phthalanes

Abstract

On exposure to a combination of Cu[I]-and Pd[0]-based catalysts, compounds such as 1 and 7 engage in tandem Ullmann−Goldberg cross-coupling and cyclopalladation-reductive elimination reactions to give benzofurans such as 8. Related reactions involving hetero-Michael additions of o-halogenated phenols or anilines to propiolates and the Pd[0]-catalyzed cyclization of the resulting conjugates provide, in a one-pot process, alternately functionalized benzofurans, indoles, or phthalanes.

Pd‐Catalyzed Annulation of β‐Iodovinyl Sulfones with 2‐Halophenols: A General Route for the Synthesis of 3‐Sulfonyl Benzofuran Derivatives

“…Based on the above experimental results and the literature precedent, a plausible mechanism for this tandem process is proposed (Scheme ). Firstly, base‐promoted oxa‐Michael addition of β‐iodovinyl sulfone ( 1 a ) with 2‐bromophenol 2 a could form enol ether ( E ‐ 3 a ).…”

“…Secondly, the mechanism starts with the consist of oxidative insertion of E-3 a to the in situ generated zerovalent palladium (PdL n ) species to form the arylpalladium complex (A). [14,21] The intra-molecular coordination with olefin moiety via π-bond complexation to form the intermediary (B). [21a] Subse-…”

“…Firstly, base‐promoted oxa‐Michael addition of β‐iodovinyl sulfone ( 1 a ) with 2‐bromophenol 2 a could form enol ether ( E ‐ 3 a ). Secondly, the mechanism starts with the consist of oxidative insertion of E ‐ 3 a to the in situ generated zerovalent palladium (PdL n ) species to form the arylpalladium complex ( A ) . The intra‐molecular coordination with olefin moiety via π‐bond complexation to form the intermediary ( B ) .…”

“…During our work being in progress, Banwell et al reported the tandem construction of benzofuran derivatives via Pd/Cu-catalyzed Ullmann-Goldberg coupling and cyclopalladation of 3-haloenones with 2-halophenols (Scheme 1a). [14] To the best of our knowledge, there is no general method for the synthesis of aryl benzofuryl sulfones. [15] Nevertheless, a general and straightforward method for the preparation of 3-sulfonyl benzofuran derivatives is high demand.…”

Construction of Diverse Dihydrodibenzofuranones by Migration/Intramolecular Arylation of Iodonium Ylides

“…9 Among these, several methods for the construction of 3,4-dihydrodibenzofuranones have also been demonstrated, which include copper-catalyzed reaction of 1,3-hexanediones with dihalobenzenes (Scheme 1(a)), 10 gold(III)-catalyzed reaction of 1,3-cyclohexanediones with o-arylhydroxylamines (Scheme 1(b)). 11 The other typical methods are also reported, which could be accessed by copper/gold-catalyzed tandem Ullmann-Goldberg cross-coupling/cyclopalladation-reductive elimination of cyclohexenones with O-iodophenol (Scheme 1(c)) 12 and transition-metal-free oxidative ring expansion of the cyclobutyl moieties (Scheme 1(d)). 13 Although several synthetic methodologies for 3,4-dihydrodibenzofuranones have been demonstrated, more general and efficient synthetic protocols are still highly needed.…”