ABSTRACT
The importance of heterocycles in many elds of science (including organic, inorganic, bioorganic, agricultural, industrial, pharmaceutical, and medicinal chemistry, as well as materials science) can hardly be overstated, and justies a long-lasting effort to work out new synthetic protocols for their production (Eicher and Hauptmann 2003). The ever-increasing awareness of the need to protect natural resources through the development of environmentally sustainable processes and the optimization of energy consumption has guided the actions of both the private and governmental sectors of society. Such a tool for this purpose that is attractive is based on ultrasound-promoted heterocyclization reactions of suitably functionalized substrates, which can allow the synthesis of highly functionalized heterocycles using readily available starting materials under mild and selective conditions. The use of ultrasound to enhance or alter chemical reactions is known as sonochemistry. Ultrasound enhances the reactivity of chemical reactions via the process of acoustic cavitation (Mason and Lorimer 2002). The assistance of ultrasonic irradiation efciently shortens the reaction times. Simple experimental procedures, very high yields, increased selectivity, and the clean reaction of many ultrasound-induced organic transformations offer additional convenience in
8.1 Introduction .................................................................................................. 217 8.1.1 Historical Background ...................................................................... 218 8.1.2 Theory ............................................................................................... 218 8.1.3 Sonochemical Synthesis of Bioactive Heterocycles ......................... 219
8.1.3.1 Sonochemical Synthesis of Three-Membered Nitrogen-Containing Heterocycles .................................... 219
8.1.3.2 Sonochemical Synthesis of Five-Membered Heterocycles .....221 8.1.3.3 Sonochemical Synthesis of Six-Membered Heterocycles .....232 8.1.3.4 Sonochemical Synthesis of Spiroheterocycles ...................240
