Palladium‐Catalyzed Carbonylative Annulation of 1‐Hydroxy‐o‐Carborane and Internal Alkynes via Regioselective B‐H Activation

Abstract

A Pd‐catalyzed three‐component carbonylative‐annulation of 1‐hydroxy‐o‐carborane, internal alkyne and carbon monoxide has been achieved via direct and regioselective cage B−H activation. A class of C,B‐substituted carborano‐coumarin derivatives with potential applications in pharmaceuticals were facilely prepared in moderate to high yields with excellent chemoselectivity and regioselectivity. A plausible reaction mechanism including CO insertion, electrophilic B−H metalation, alkyne insertion and reductive elimination was proposed.

A Review of Synthetic Application of Homogeneous, Heterogenised‐Homogeneous, and Microwave‐Assisted Catalytic Carbonylation of Selected Substrates

“…The product has excellent chemoselectivity and regioselectivity. [53] Starting from o-iodophenol (0.5 mmol) or N-substituted oiodoanilines (0.5 mmol) and internal alkynes (2.5 mmol), Kadnikov and his colleagues discussed carbonylative annulation. In the selected reaction condition, Pd(OAc) 2 (0.5 mmol) and n-Bu 4 NCl (0.5 mmol) were taken with CO in DMF at 100-120 °C.…”

Ir-Catalyzed Selective B(3)-H Amination of o-Carboranes with NH3

“…The extraordinary properties of carboranes including icosahedral geometry, three-dimensional aromaticity, and inherent robustness endow them a wide range of applications, yet make their functionalization quite challenging. In view of the considerable progress recently made in transition-metal-catalyzed vertex-specific functionalization of carboranes, ,, we hypothesized that acceptorless dehydrogenative cross-coupling between NH 3 and carborane would provide facile access to the desired aminocarborane derivatives. These compounds can only be synthesized through a reduction-nucleophilic amination–oxidation process with the risk of explosion or a tandem route including transition-metal-catalyzed B-H amination and subsequent deprotection. , In sharp contrast to the strong coordination of NH 3 to BH 3 in amine-borane adducts, no significant interactions between NH 3 and carborane exist, increasing the difficulty of the proposed dehydrogenative cross-coupling.…”

Iridium-Catalyzed Annulation of o-Carboranyl Carboxylic Acids with Alkynes: Synthesis of Carborano-Isocoumarins

“…We have developed two methods to prepare this class of molecules. One was based on iridium-catalyzed cascade dehydrogenative cross-coupling of 1-COOH- o -carborane with benzoic acids (Scheme b), and another was a palladium-catalyzed three-component carbonylative annulation (Scheme c) . We speculated that an iridium-catalyzed formal [4+2] annulation of carboranyl carboxylic acids with alkynes could be achieved for the synthesis of carborano-isocoumarin derivatives on the basis of our earlier work on Ir-catalyzed selective B(4)-alkenylation of o -carborane by alternating the reaction path .…”

“…One was based on iridium-catalyzed cascade dehydrogenative cross-coupling of 1-COOH-o-carborane with benzoic acids (Scheme 1b), 13 and another was a palladium-catalyzed three-component carbonylative annulation (Scheme 1c). 14 We speculated that an iridium-catalyzed formal [4+2] annulation of carboranyl carboxylic acids with alkynes could be achieved for the synthesis of carborano-isocoumarin derivatives on the basis of our earlier work on Ir-catalyzed selective B(4)-alkenylation of o-carborane by alternating the reaction path. 15 According to the reaction mechanism proposed for the synthesis of 1-R-4-alkenyl-o-carboranes (4) shown in the catalytic cycle 1 of Scheme 2, 15 we anticipated that the intermediate C could possibly undergo reductive elimination to afford 3 and [Cp*Ir(I)] under appropriate reaction conditions via catalytic cycle 2 in Scheme 2.…”