Solvent-free reaction as green chemistry for the synthesis of substituted tetrahydrocarbazoles by oxalic acid catalyst.

Thrust in the preparation of new heterocyclic molecules is increasing due to their proven significant biological activities1. The paramount importance of heterocycles such as indoles and their derivatives in natural product chemistry and pharmacology constantly drives the search for the new procedures for their construction and also for the preparation of variety of their derivatives to exploit their useful biological activities. Substituted tetrahydrocarbazoles belongs to the class of indole alkaloids that have been reported to possess an array of biological properties2.In general the carbazoles synthesis is carried out by multistep Fisher reaction3 which requires the usage of organic solvents with very meager product yields. Hence a simple and efficient method for the synthesis of these pharmaceutically important class of compounds is highly desirable precluding the usage of organic solvents. Initially Substituted phenyl Hydrazine‘s were used to optimize the reaction conditions such as different acids, solvents, and reaction temperature. Among, several Acids were tested, finally we found that oxalic acid catalyst and solvent-free conditions given excellent yields. Various substituted phenyl hydrazine have been reacted with cyclohexanone in the presence of oxalic acid catalyst at C to obtain the final product in high yields,mild reaction condition and green synthesis in solvent-free condition.(Scheme1)