Applications of CeCl3.7H2O-NaI System Towards the Formation of Heterocyclic Structures

Applications of CeCl3\ub77H2O-NaI system towards the formation of heterocyclic structures Enrico Marcantoni,1 Massimo Massaccesi,1 Marino Petrini,1 Giuseppe Bartoli,2 Letizia Sambri2 1 Department of Chemical Sciences, University of Camerino, via S. Agostino 1, I-62032 Camerino (MC), Italy 2 Department of Organic Chemistry \u201cA. Mangini\u201d, University of Bologna, V.le Risorgimento 4, I-40136, Bologna, Italy massimo.massaccesi@unicam.it CeCl3\ub77H2O-NaI system has emerged in the last years as a \u201cfriendly\u201d Lewis acid,(1) able to promote a wide range of organic transformations. Its high and specific affinity for O-containing functionalities prompted us to employ such a promoter in the field of heterocyclic chemistry. We present some our recent applications of CeCl3\ub77H2O-NaI combination directed towards the formation of heterocyclic systems, within an organic synthetic view. Continuing our work on solvent-free conditions, we found that CeCl3\ub77H2O-NaI system supported on silica gel promotes the addition of a variety of indoles 1 to nitroalkenes 2, giving 2-indolyl-1-nitroalkanes 3 in good yields.(2) Our methodology was applied to the synthesis of β-carbolines 4, a large group of naturally occurring heterocyclic alkaloids.(3) The tetrahydro-2H-pyran heterocyclic structure (THP) is frequently used for the protection of alcohols in organic synthesis. We have developed a practical procedure for the introduction of THP group by using the CeCl3\ub77H2O-NaI system. After screening various reaction conditions, we found that 3,4-dihydro-2H-pyran ring reacts with the hydroxy function in the presence of a catalytic amount of CeCl3\ub77H2O-NaI, for the conversion of alcohols into the corresponding THP ethers 5. The scope of the reaction was investigated through several examples, which revealed both the chemoselective action of our Lewis acid system and its marked capacity to act as a promoter even in solvent-free conditions. (1) Bartoli, G.; Marcantoni, E.; Sambri, L. Synlett. 2003, 14, 2101; (2) Bartoli, G.; Bosco, M.; Giuli, S.; Giuliani, A.; Lucarelli, L.; Marcantoni, E.; Sambri, L.; Torregiani, E. J. Org. Chem. 2005, 70, 1941; (3) Cacchi, S.; Fabrizi, G.; Parisi, L. M. Org. Lett. 2003, 5, 3843; Wang, H.; Usui, T.; Osada, H.; Ganesan, A. J. Med. Chem. 2000, 43, 1577