Recent Advances in Microwave‐assisted Cross‐Coupling Reactions

Abstract

The carbon-carbon and carbon-heteroatom bond forming coupling reactions have a fundamental value for the organic chemistry, and, therefore, these reactions have been always among the most valuable and basic studies for the evolution of organic synthesis and are extensively used for the synthesis of practically valuable compounds. Currently, greener techniques have been pulled in the consideration of researchers due to the rising environmental concern. Nowadays, the modern synthetic chemists of both academia and industry are trying to design the desired target molecules by using eco-friendly methods. In this context, microwaveassisted organic synthesis (MAOS) is known as one of the most convenient and emerging technologies in synthetic chemistry. Microwave activation/heating is a very convenient technique from the viewpoint of green chemistry because it speeds up the reaction rates and provides a higher yield by reducing side reactions. The present review represents the literature survey from 2008 to 2021 that covers the latest trends of microwave-assisted CÀ C and CÀ heteroatom bond forming coupling reactions with greener prospects.

Recent Advances in the Synthesis of 5-(Hetero)aryl Uracil Derivatives

“…Template for SYNLETT Thieme In 2012, the first Suzuki-Miyaura reaction in water was reported by the Sartori group using a Na2PdCl4/TPPTS (sodium triphenylphosphine trisulfonate) as a water-soluble combination (Figure 7). 41 Compared with Len's work, [36][37][38][39] this coupling utilized both electron-rich and poor types of aryl boronic acids, affording the unprotected deoxyuracils 15 in 18-77% yields. The authors also discovered that TPPTS was not even required when the reaction was conducted at 100 o C, and the loading of palladium catalyst may be reduced to 0.01 mol%, although with much longer reaction times (24 hours).…”

“…36 This environmentally-friendly and cost-effective method employed water as the solvent, eliminated the need for protection or deprotection steps with the ribose hydroxyls, and used minimal palladium loading (as low as 0.05 mol%). 37 Subsequently, the same group devised a straightforward deglycosylation technique employing microwave irradiation at 200 o C in pure water, yielding 5-aryluracil analogues. [38][39] Figure…”

“…35 This environmentally friendly and cost-effective method employed water as the solvent, eliminated the need for protection-deprotection steps of the ribose hydroxy groups, and used a minimal palladium loading (as low as 0.05 mol%). 36 Subsequently, the same group devised a straightforward deglycosylation technique employing microwave irradiation at 200 °C in pure water, yielding 5-aryluracil analogues. 37,38 Scheme 3 Suzuki-Miyaura coupling under microwave irradiation Shih and Chien reported a direct route to various 5-and 6-aryl-substituted uridine derivatives 17 through a Suzuki-Miyaura cross-coupling reaction of ribose-protected uracils 16 with arylboronic acids (Scheme 4).…”

“…[40][41][42] Later, a similar coupling reaction in water (without the addition of organic solvents) was first reported by the Sartori group, who used a modified system with Na 2 Pd-Cl 4 as the catalyst (Scheme 5). 43 Compared with Len's work, [35][36][37][38] this coupling utilized both electron-rich and electron-deficient arylboronic acids, affording the unprotected deoxyuracils 15 in yields of 18-77%. The group also discovered that TPPTS was not even required when the reaction was conducted at 100 °C, and the loading of palladium catalyst could be reduced to 0.01 mol%, although with a much longer reaction time (24 hours).…”

Cross‐Coupling Between Aryl Halides and Aryl Alkynes Catalyzed by an Odd Alternant Hydrocarbon

“…[12,13] As a result, various reports are known for Sonogashira coupling reactions under palladium metal-free conditions, using copper , [14,15] iron , [16,17] cobalt , [17] ruthenium [18] and Ni [19,20] catalysts resulting in the cross-coupling between aryl halides and terminal alkyne partners (Figure 1a). Furthermore, several heterogeneous transition metal-based catalytic procedures [21,22] have also been explored for this cross-coupling reaction which generally operates at higher temperatures or under microwave [23,24] /photostimulation. [25] Though not catalytically, a handful of C(sp)À C(sp 2 ) cross-couplings have been explored in several transition metal-free stoichiometric methods earlier.…”