Suzuki-Miyaura coupling microwave-assisted

More recently, Ktigtikbay and co-workers investigated the microwave-assisted Suzuki-Miyaura coupling of 2- and 3-halopyridines using a PdfOAcl /benzimidazo-lium salt catalyst system and K COj as the base. All complexes were reported to have similar activity with the exception of complex 93, which was found to be the least active in Suzuki-Miyaura coupling. In general, heteroaryl chlorides were found to be less reactive than the bromide analogs. In addition, 3-halopyridines were found to couple more efficiently than 2-halopyridines (Table 4). 

Table 4 Microwave-assisted Suzuki-Miyaura coupling of 2- and 3-halopyridines... 

A facile synthesis of some new substituted aryl and heteroarylflavones by thermal and microwave-assisted Suzuki-Miyaura coupling reaction was also carried out (Joshi and Hatim, 2012). 

General microwave assisted Suzuki-Miyaura cross-coupling procedure... 

It is noteworthy that the microwave-assisted Suzuki-Miyaura reactions were found to be far superior to the reactions under conventional heating, as can be demonstrated by yield improvements from 22% to 84% in the case of cross-coupling of PEA derivatives. Microwave-irradiation also provided smooth conversions in water as the sole solvent. 

SAR studies were performed on compoimds containing the 9H-isothia-zolo[5,4-fc]quinoline-3,4-dione (ITQ) nucleus and it was found that some of them are potent antibacterial agents (see Scheme 101) [114,115]. They were prepared from compound 353, which was treated with cyclopropyl isothiocyanate in DMF and then with Mel. Compound 354 (94%) was obtained and treated with in NaH in DMF to give the isothiazolo[ 5,4-fo] quinoline compound 355 (93%). Its treatment with anhydrous NaSH gave the corresponding mercaptan (84%), which was directly cychsed without purification to 356 (85%) in the presence of hydroxylamine-O-sulfonic acid. Microwave-assisted Suzuki-Miyaura cross-coupling of the ITQ nucleus 356 with the desired aryl-boronic esters or acids afforded derivatives 357, typically, in 30-50% yield after HPLC purification (Scheme 87). 

Microwave-assisted Suzuki-Miyaura cross-coupling reaction has been used for the generation of aza-analogs of the natural product Steganacin (Chapman and Thompson, 2007). It was reported that the application of microwave irradiation was highly beneficial for the biaryl coupling of electronically rich aryl bromides with some substituted o-formylphenylboronic acids (Beryozkina et al., 2006). 

The time consuming chromatographical purification of heterocycles 28 and 29 slowed down the rate of library production. A phase separation using fluorous chemistry was employed by Zhang and Lu to address the workup and purification of fused 3-aminoimidazo[ l,2-a]pyridines (such as 30) [54]. Thus, attachment of a perfluorooctanesulfonyl tag to aldehydes and subsequent Ugi three-component microwave-assisted condensations with 2-aminopyridines and isocyanides furnished the desired heterocycles 30, which were conveniently isolated by fluorous solid-phase extraction. The fluorous tag could be subsequently used as an activating group in the post-condensation modifications, such as Suzuki-Miyaura cross-coupling reactions. 

A microwave-assisted tandem Ir-catalyzed C-H boronylation/Pd-catalyzed Suzuki-Miyaura cross-coupling reaction has been reported (Harrisson et al., 2009). This includes the synthesis of arylboronic acids, direct boronylation of arenes and alkanes, which provides access to synthetically useful compounds without relying on the accessibility of aryl or alkyl halides. They developed an elegant methodology for the direct C-H boronylation using a pinacoldiborane dimer under microwave irradiation at 80°C for 5-60 min. 

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