Microwave‐Promoted Suzuki–Miyaura Cross‐Coupling of Aryl Imidazolylsulfonates in Water

Abstract

Aryl imidazol-1-ylsulfonates are efficiently cross-coupled with potassium aryl-and alkenyltrifluoroborates in neat water under microwave heating (40 W, 110 8C) using 0.5 mol% of oxime palladacycle 1a, hexadecyltrimethyl ammonium bromide (CTAB) as additive, and triethylamine as base. Under these simple phosphane-free reaction conditions a wide array of biaryl, stilbene and styrene derivatives has been prepared in good to high yields and with high regio-and diastereoselectivities in only 30 min.

Microwave‐Promoted Copper‐Free Sonogashira–Hagihara Couplings of Aryl Imidazolylsulfonates in Water

“…Lower yields were achieved in the coupling with the electron-poor 4-(trifluoromethyl)phenyl-, and 2-pyridyl acetylene ( Table 2, entries 4 and 5), results which were also observed for alkyl substituted acetylenes such as cyclohexyl acetylene (63%, entry 6) and 1-butyne (40%, entry 7). In the case of using trimethylsilylacetylene as nucleophile, a double arylation process was observed affording 1,2-di(naphthalen-1-yl)ethyne (15) as major product in a 45% isolated yield ( Table 2, entry 8). Unfortunately, this yield could not be improved by using two equivalents of electrophile, conditions which afforded 15 in a poor 15% yield.…”

“…a) Isolated yield after flash chromatography. b) Isolated yield for 1,2-di(naphthalen-1-yl)ethyne (15). c) A 7% yield (GC) of trimethyl(naphthalen-1-ylethynyl)silane (4h) was also detected in the crude reaction mixture.…”

“…[13] This coupling can be also performed in neat water by using the cationic surfactant [14] hexadecyltrimethyl ammonium bromide (CTAB) as additive, which has allowed to cross-couple aryl imidazol-1-ylsulfonates with potassium aryl-and alkenyltrifluoroborates under microwave heating (40 W, 110 ºC) using 0.5 mol% of oxime palladacycle 1a. [15] To date, no examples have been reported for transition-metal catalyzed Sonogashira crosscoupling of phenol derivatives in neat water (Scheme 1). [16] In this communication, we present the first Sonogashira coupling of aryl imidazolylsulfonates performed in neat water using oxime palladacycle 1a as precatalyst under microwave irradiation (Scheme 1).…”

Synthesis and reactivity of imidazole-1-sulfonate esters (imidazylates) in substitution, elimination, and metal-catalyzed cross-coupling reactions: a review

“…Recently, Nájera and co-workers also reported the Suzuki-Miyaura coupling of aryl imidazylates with potassium aryl-and alkenyltrifluoroborates. [58] All of the electron-rich, electron-poor, sterically hindered, and hetero cyclic imidazylates showed good reactivity in this phosphane-free reaction (Scheme 14).…”

Copper‐Free Oxime–Palladacycle‐Catalyzed Sonogashira Alkynylation of Deactivated Aryl Bromides and Chlorides in Water under Microwave Irradiation

“…[12] Specially interesting has resulted those couplings performed using neat water as solvent and deactivated electrophiles such as aryl chlorides (Suzuki reaction [13] ) and aryl imidazolylsulfonates (Suzuki [14] and Sonogashira [6] reactions) in the presence of surfactants. 7h,7l In continuation of our exploration on the application of oxime palladacycles under green conditions, we herein describe the Sonogashira coupling reaction of deactivated aryl bromides and chlorides in water under microwave irradiation.…”