Microwave Chemistry Highlights
Microwave-Assisted Suzuki Couplings with Simultaneous Cooling
Suzuki-couplings using a microencapsulated palladium catalyst (Pd EnCat) under microwave heating were investigated by the group of Steven V. Ley at the University of Cambridge (Chem. Eur. J. 2006, 12, 4407. ). For those compounds giving low purities under conventional microwave conditions A, higher purities could be achieved by performing the reactions at 50 W (reaction temperature did not exceed 76 °C) with simultaneous cooling (compressed air, B) by preventing otherwise occurring thermal decompositions. Even higher purities were obtained by conducting the reactions via a flow-through approach again in combination with cooling (C) due to shorter reaction times (ca. 1 min) and therefore diminished side reactions.
Microwave-Assisted Cu(II)-Mediated Cross-Couplings with Simultaneous Cooling
Erik Van der Eycken and co-workers from University of Leuven performed Cu(II)-mediated scaffold decorations on the pyrazinone core (Org. Lett. 2006, 8, 1863. ). N-Arylations utilizing arylboronic acids applying the Chan-Lam protocol were successfully conducted under microwave heating (300 W) with intensive simultaneous cooling at 0 °C (Coolmate). Due to prevented product decomposition, excellent yields could be achieved compared to reactions at rt or elevated temperatures, respectively. High yields could be obtained by using a mixture of Et3N/pyridine (1:2) as opposed to Et3N alone: 93% compared to 69% for R = 3-CF3.