Synthesis of More Complex or Polyheterocyclic Systems

The purpose of this section is to highlight the applications of microwave irradiation to syntheses of more complex or polyheterocyclic systems. When conventional thermal procedures (metal or oil bath) fail microwave irradiation can be used as an alternative to classical methods enabling development of easy and rapid access to new heterocycles irrespective of the conditions needed in the homogeneous phase. 

R = Ph, 2-pyridyl, 2-furyl R = 2-oxazolyl, 2-pyrimidyl, 1-Me-5-pyrazolyl, 2-tetrahydrofutyl, 5-(1,2,3-triazolyl), 4-thiazolyl, 2-pyridyl, morpholino 

A new means of access to 5a,10,14fo,15-tetraazabenzo[a]indeno[l,2-c]anthracen-5-ones 33 and to benzimidazo[l,2-c]quinazoline 34 was reported in 2000 [110]. The preparation of 6-mercapto-benzimidazo[l,2-c]quinazoline (34) was easily ac- 

Step starting material Product Conventional heating Microwave irradiation  

5-Deaza-5,8-dihydropterins were prepared from 2,6-diaminopyrimidin-4-one, 1,3-dicarbonyl compounds, or benzoylacetonitrile, and aromatic or aliphatic aldehydes [115]. This three-component cyclocondensation proceeds under microwave-assisted conditions in good yield using Zn(II) bromide as a Lewis acid catalyst, and with total control of regiochemistry. 

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