Suzuki reaction microwave-assisted synthesis

A one-pot synthesis of thiohydantoins has been developed using microwave heating [72]. A small subset of p-substituted benzaldehydes, prepared in situ from p-bromobenzaldehyde by microwave-assisted Suzuki or Negishi reactions, was reacted in one pot by reductive amination followed by cyclization with a thioisocyanate catalyzed by polystyrene-bound dimethyl-aminopyridine (PS-DMAP) or triethylamine, all carried out under microwave irradiation, to give the thiohydantoin products in up to 68% isolated yield (Scheme 16). 

A recent publication by the group of Barbarella has disclosed the rapid preparation of poorly soluble unsubstituted and modified a-quinque- and sexithiophenes by the extensive use of bromination/iodination steps and microwave-assisted Suzuki and Sonogashira cross-couplings (Scheme 6.16) [42]. Suzuki reactions were either carried out under solvent-free conditions on a strongly basic potassium fluoride/ alumina support for the synthesis of soluble oligothiophenes, or in solution phase for the preparation of the rather insoluble a-quinque- and sexithiophenes. In both cases, 5 mol% of [l,l -bis(diphenylphosphino)ferrocene]dichloropalladium(II)... 

The synthesis of fully conjugated semiconducting para-phenylene ladder polymers by microwave-assisted palladium-mediated double Suzuki and Stille-type reactions has been demonstrated by Scherf and coworkers (Scheme 6.27) [58], The procedure, which yields polymeric material in ca. 10 min, has no adverse effects on the quality of the polymers and displays a high degree of reproducibility. Compared... 

Baxendale IR, Griffiths-Jones CM, Ley SV, Tranmer GK (2006b) Microwave-assisted Suzuki coupling reactions with an encapsulated palladium catalyst for batch and continuous-flow transformations. Chem Eur J 12 4407-4416 Baxendale IR, Deeley J, Griffiths-Jones CM, Ley SV, Saaby S, Tranmer GK (2006c) A flow process for the multi-step synthesis of the alkaloid natural product oxomaritidine a new paradigm for molecular assembly. J Chem Soc Chem Commun 2566-2568... 

Some synthetic approaches to pyrazines relied on metal-assisted reactions. A synthesis of 6-substituted 5H-pyrrolol2,3-bJpyrazines via Pd-catalyzed heteroannulation from W-(3-chloropyrazin-2-yl)methanesulfonamide and alkynes was developed <04TL8087>, and 3- and 5-substituted 2(l//)-pyrazinones were prepared by Suzuki and Heck reactions using 3,5-dichloro-2(l//)-pyrazinones <04TL1885>. An improved synthesis of 6-substituted-5//-pyrrolo 2,3-iiJ-pyrazines via microwave-assisted Pd-catalyzed heteroannulation was developed <04TL8631>, and the reaction of a-diazo-P-keto esters with Boc amino acid amides in the presence of a Rh catalyst gave, after air oxidation, pyrazin-6-ones 111, which were then converted into tetrasubstituted pyrazines 112 <04OL4627>. 

Unprotected 4-heteroaryl phenylalanines have been prepared by microwave-assisted Suzuki-Miyaura reactions. Amino adds containing the biaryl motif have several interesting applications in medicinal chemistry and this method enabled their synthesis without protection of the amino acid. Optically pure boronic acids could be used without racemization (Scheme 15.16) [49]. 

Polyethylene glycol (PEG) is an inexpensive, non-toxic reaction medium for the microwave-assisted Suzuki cross-coupling of arylboronic acids with aryl halides. This environmentally friendly microwave protocol offers ease of operation and enables recyclability of catalyst in the synthesis of various substituted biaryls, employing palladium chloride as catalyst and potassium fluoride as the base (Equation 92) [135]. 

Lepine and Zhu accomplished total synthesis featuring judicious use of the PTC 1-catalyzed asymmetric alkylation of Schiff base 1 and a microwave-assisted intramolecular Suzuki-Miyaura reaction for the formation of... 

Lepine R, Zhu J. Microwave-assisted intramolecular Suzuki—Miyaura reaction to macrocycle, a concise as3mimetric total synthesis of biphenomycin B. Org. Lett. 2005 7 (14) 2981-2984. 

In Suzuki reaction, cross-coupling of aryl- or vinyl-boronic acid with an aryl or vinyl halide catalyzed by a palladium complex, is one of the most versatile reactions for the construction of carbon-carbon bonds, in particular for the formation of biaryls. Recent developments have expanded the possible applications of this reaction enormously. Microwave-assisted Suzuki reactions can now be performed in many different ways and have been incorporated into a variety of challenging synthesis. Under microwave-heated condition, the Suzuki coupling of aryl chlorides with bo-ronic acids was performed in an aqueous media using the air and moisture-stable palladium catalyst. A drastic reduction of the reaction time to 15 min and the formation of products in good yields were achieved (Miao et al, 2005). 

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