Palladium-catalyzed Sonogashira coupling reactions in γ-valerolactone-based ionic liquids

Abstract

It was demonstrated that the γ-valerolactone-based ionic liquid, tetrabutylphosphonium 4-ethoxyvalerate as a partially bio-based solvent can be utilized as alternative reaction medium for copper- and auxiliary base-free Pd-catalyzed Sonogashira coupling reactions of aryl iodides and functionalized acetylenes under mild conditions. Twenty-two cross-coupling products were isolated with good to excellent yields (72–99%) and purity (>98%). These results represent an example which proves that biomass-derived safer solvents can be utilized efficiently in common, industrially important transformations exhibiting higher chemical and environmental efficiency.

A facile protocol for copper‐free palladium‐catalyzed Sonogashira coupling in aqueous media

“…Further attempts with Pd(dppf)Cl 2 and Pd 2 (dba) 3 showed no advantage in catalytic efficiency under the similar conditions (Table 1, entries 10–11). These results strongly suggested that the phosphine ligand was necessary for the successful completion of CC bond formation in the examined system consistent with a previous study 12 . Therefore, an excess amount of acetylene, mild reaction conditions (40 °C), and a catalytic amount of Pd(PPh 3 ) 2 Cl 2 were identified as the ideal reaction parameters for the successful C sp C sp2 bond formation via Cu‐free coupling reaction (Table 1, entry 3).…”

“…With this aim, several studies on the Pd‐catalyzed Sonogashira coupling reaction have been performed in RTILs. For instance, Mika et al reported recently a Cu‐free Pd‐catalyzed Sonogashira coupling in γ‐valerolactone‐based ionic liquids 12 . Other ionic liquids (ILs), such as [BMIM][PF 6 ], 13 [BMIM][BF 4 ], 14 and pyridine‐based ILs, 15 have also been utilized in Cu‐free Sonogashira coupling reactions.…”

Tetrabutylphosphonium 4-ethoxyvalerate as a biomass-originated media for homogeneous palladium-catalyzed Hiyama coupling reactions

“…When different precursors were compared, it was revealed that using of bis(triphenylphosphine)palladium(II) dichloride (Pd(PPh 3 ) 2 Cl 2 ) and tris(dibenzylideneacetone)dipalladium(0) (Pd 2 (dba) 3 ) gave acceptable yields of 3a (Table 2, entries 1 and 5). A similar observation was reported for the Sonogashira reaction performed in biomass-originated ILs (Orha et al 2019).…”

“…To demonstrate their further applicability, they were first compared to the conventional 1-butyl-3-methylimidazolium cation-based ILs in the coupling of iodobenzene (1a) and triethoxyphenylsilane (2a) as a model reaction (Scheme 1) under typically used "Hiyama conditions" using tetrabutylammonium fluoride as a F − source (Ismalaj et al 2014). As with Sonogashira coupling in ILs (Orha et al 2019), negligible conversion rates of 1a were detected in butylmethylimidazolium cation containing ILs (Table 1 entries 1-3). The reaction efficiency could be significantly increased by the introduction of tetrabutylphosphonium 4-ethoxyvalerate [TBP][4EtOV], resulting in the conversion of 1a.…”

“…The GVL-based [TBP][4EtOV] ionic liquid has been proven as an excellent reaction media for transition-metalcatalyzed C-N (Ullmann type) (Orha et al 2018) and C-C (Sonogashira) (Orha et al 2019) coupling reactions previously. In the present work, we demonstrated that its utilization can be extended for Hiyama coupling, as well, which makes it an attractive biomass-based, environmentally friendly alternative for common, fossil-based solvents, and opens the possibility for its application in wider range of chemical transformations.…”