Microwave phase synthesis

Other PK variations include microwave conditions, solid-phase synthesis, and the fixation of atmospheric nitrogen as the nitrogen source (27—>28). Hexamethyldisilazane (HMDS) is also an excellent ammonia equivalent in the PK synthesis. For example, 2,5-hexanedione and HMDS on alumina gives 2,5-dimethylpyrrole in 81% yield at room temperature. Ammonium formate can be used as a nitrogen source in the PK synthesis of pyrroles from l,4-diaryl-2-butene-l,4-diones under Pd-catalyzed transfer hydrogenation conditions. 

Solid-Phase Methods for the Microwave-Assisted Synthesis of Heterocycles... 

Since 1986, when the very first reports on the use of microwave heating to chemical transformations appeared [147,148], microwave-assisted synthesis has been shown to accelerate most solution-phase chemical reactions [24-27,32,35]. The first application of microwave irradiation for the acceleration of reaction rate of a substrate attached to a solid support (SPPS) was performed in 1992 [36]. Despite the promising results, microwave-assisted soHd-phase synthesis was not pursued following its initial appearance, most probably as a result of the lack of suitable instriunentation. Reproducing reaction conditions was nearly impossible because of the differences between domestic microwave ovens and the difficulties associated with temperature measurement. The technique became a Sleeping Beauty interest awoke almost a decade later with the publication of several microwave-assisted SPOS protocols [37,38,73,139,144]. There has been an extensive... 

Fig. 10 Liberty (CEM Corporation), the first automated microwave solid-phase peptide synthesizer, is shown on the left-, the available reaction vessel setup for solid-phase synthesis is depicted on the right...

Representative examples of the recent applications of controlled microwave heating in solid-phase synthesis of heterocychc compounds are summarized. The preparation of monocyclic compoimds is presented hrst, followed by a description of the synthesis of polycyclic structures. 

Microwave-Promoted Synthesis of Bicyclic Pyrimidine Derivatives on Solid-Phase... 

Fig. 26 Solid-phase synthesis of indol-2-ones by microwave-assisted radical cyclization. Reagents and conditions a NaH, DMF b BusSnH, AIBN, DMF, MW 170 °C, 45 min, sealed vessel c 10% TFA in CH2CI2. R = H, F, Me, OCF3 R = Phe, 3-OMe - Phe, 4-Me - Phe, 3,4-0CH20-Ph, (CH2)4, diMe R" = H, Me R " = H, Me...

In most cases, the overall synthesis time was greatly reduced (from hours or days to minutes) by switching from conventional to microwave heating, facilitating the rapid preparation of novel chemical entities. The combination of soUd-phase synthesis with microwave irradiation also allowed access to a few classes of molecules that had proven elusive via other synthetic strategies (traditional solution-phase synthesis). 

Abstract An overview on the microwave-enhanced synthesis and decoration of the 2(lH)-pyrazinone system is presented. Scaffold decoration using microwave-enhanced transition-metal-catalyzed reactions for generating structural diversity, as well as the conversion of the 2(lH)-pyrazinone skeleton applying Diels-Alder reactions to generate novel heterocyclic moieties are discussed. The transfer of the solution phase to polymer-supported chemistry (SPOS) is also described in detail. 

Erd lyi M (2006) Solid-Phase Methods for the Microwave-Assisted Synthesis of Heterocycles. 1 79-128... 

---