Efficient preparation of 2-indolyl-1-nitroalkane derivatives employing nitroalkenes as versatile Michael acceptors: new practical linear approach to alkyl 9h-beta-carboline-4-carboxylate.

The combination of cerium(III) chloride heptahydrate and sodium iodide supported on silica gel is known to promote Michael-type additions. Continuing our work on solvent-free conditions, the CeCl3.7H2O-NaI-SiO2 system catalyzes the addition of a variety of indoles and nitroalkenes, giving 2-indolyl-1-nitroalkane derivatives in good yields. Development of this method has resulted in a new protocol for the synthesis of 4-substituted beta-carbolines.