Ultrasound promoted synthesis of spirocyclohexanones catalyzed by proline

Spirocyclic compounds have surprised synthetic chemists for more than a halfcentury. These compounds have significant conformational features and structural implications for biologically important natural products [1]. The Michael addition reaction is one of the most powerful method for C-C bond formation in current synthetic organic chemistry specifically intermolecular double- Michael reactions are the most useful tool for constructing spirocyclic products from the noncyclic substances [2]. There have been an increasing number of reports on the synthesis of organic compounds in the presence of ultrasonic waves with higher yields, shorter reaction times, and milder conditions than the classical methods. It has also been found that the separation of the product in the ultrasonic technique is more easier and efficient than conventional methods [3]. Hence, as mentioned above, herein, synthesis of various spirocyclohexanones from arylidine acetons, which were prepared by aldol condensation between oneequivalent acetone and two equivalent arylaldehydes , and (thio) barbituric acid in different conditions were investigated. The results showed that the highest yields(88%) were obtained in the presence of catalytic amount of proline (25%) in EtOH, as a green solvent, at 70 oC under ultrasonic irradiation. Changing the catalyst to loweror higher amounts led to sharp decreases in the reaction results. The reaction is diastereoselective and only cis isomers were achieved in high yields. Finally, the products were purified by washing with water and EtOH. So, using ultrasound not only allows rapid and clean conversion but also simplifies experimental setup and workup leading to rapid generation of spirocyclohexanone without chromatography and even recrystallization.