Palladium-Catalyzed C2-Selective Oxidative Olefination of Benzo[b]thiophene 1,1-Dioxides with Styrenes and Acrylates

Abstract

Here, we disclose a novel Pd(II)-catalyzed oxidative Heck reaction of benzo[b]thiophene 1,1-dioxides with styrenes and acrylates. This transformation features broad functional group tolerance and high C2 selectivity. Furthermore, the photoluminescence properties of C-2 alkenylated products have been characterized, which illustrates the potential usefulness of our protocol in constructing π-conjugated fluorescent molecules.

Palladium-Catalyzed C2-Selective Direct Arylation of Benzo[b]thiophene 1,1-Dioxides with Arylboronic Acids

“…Finally, a plausible mechanism for the Pd­(II)-catalyzed C–H bond oxidative cross-coupling was proposed (Scheme ). , First, the cyclopalladium intermediate IM1 was obtained via the C–H activation of benzo­[ b ]­thiophene 1,1-dioxide 1a . Next, phenylboronic acid 2a is coordinated with pyridine to give the triphenylboroxine pyridine complex 7 .…”

“…Thiophene 1,1-dioxide derivatives were prepared according to the literature procedures. 15 Arylboronic acids were purchased from Energy Chemical. DCE, DMF, and DMSO were dried by refluxing over CaH 2 .…”

“…Afterward, the N-chelator-assisted C–H/C–H dehydrogenative coupling strategy was used in the formation of extended heteroaromatic conjugated molecules (Scheme b) . Very recently, we reported the Pd­(II)-catalyzed oxidative olefination reaction of benzo­[ b ]­thiophene 1,1-dioxides with alkenes based on the C–H activation pathway (Scheme c) . Following our continued interest in the transformation of thiophene 1,1-dioxide compounds, we herein disclose a novel Pd­(II)-catalyzed direct arylation of benzo­[ b ]­thiophene 1,1-dioxides with arylboronic acids for the synthesis of aryl-substituted benzo­[ b ]­thiophene 1,1-dioxides.…”

“…14 Very recently, we reported the Pd(II)-catalyzed oxidative olefination reaction of benzo [b]thiophene 1,1-dioxides with alkenes based on the C−H activation pathway (Scheme 1c). 15 Following our continued interest in the transformation of thiophene 1,1-dioxide compounds, we herein disclose a novel Pd(II)-catalyzed direct arylation of benzo [b]thiophene 1,1-dioxides with arylboronic acids for the synthesis of aryl-substituted benzo [b]thiophene 1,1-dioxides. The efficient reaction took place at the C2position via C−H activation, followed by a Pd(II)-catalyzed direct arylation process (Scheme 1d).…”

Palladium Catalysis: Dependence of the Efficiency of C−C Bond Formation on Carboxylate Ligand and Alkali Metal Carboxylate or Carboxylic Acid Additive. Part A: the C(sp2)−C(sp2), C(sp2)−C(sp3) and C(sp3)−C(sp3) Bonds

“…[138b] Recently, Huang and co-workers disclosed the DHR of benzo[b]thiophene 1,1-dioxide with styrene using various Pd and Ag carboxylates, carboxylic acids and solvents (Scheme 20e). [139] The best result arose in THF with Pd(OAc) 2 , t-BuCO 2 Ag and t-BuCO In dioxane, the cross-coupling of 6-methylchromen-4-one [68] with benzoquinone under Pd-(OAc) 2 catalysis in the presence of AgOAc occurred in modest yield which was greatly improved with t-BuCO 2 H additive, but use of t-BuCO 2 H as the solvent was detrimental to the process (Scheme 21). [140] The formation of tert-butyl 3-(1-methyl-4-oxo-1,4-dihydroquinolin-3-yl)acrylate from 1-methyl-2,3-dihydroquinolin-4-one and tert-butyl acrylate under Pd(OCOCF 3 ) 2 catalysis arose from a domino reaction -dehydrogenation [141] leading to 1-methylquinolin-4-one, activation of its C3À H bond [68] and finally Heck-type reaction with the acrylate [142] -which provided the best yield in t-BuCO 2 H instead of dioxane or AcOH and using CuCO 3…”