Indium-Catalyzed Regioselective ?-Alkylation of Pyrroles with Carbonyl Compounds and Hydrosilanes and Its Application to Construction of a Quaternary Carbon Center with a ?-Pyrrolyl Group.

Title Indium-Catalyzed Regioselective ?-Alkylation of Pyrroles with Carbonyl Compounds and Hydrosilanes and Its Application to Construction of a Quaternary Carbon Center with a ?-Pyrrolyl Group.
Authors S. Nomiyama; T. Ogura; H. Ishida; K. Aoki; T. Tsuchimoto
Journal J Org Chem
DOI 10.1021/acs.joc.7b00446
Abstract

Treatment of N-substituted pyrroles with carbonyl compounds and nucleophiles under indium catalysis was found to be a promising method for preparing ?-alkylpyrroles without contamination by ?-alkylpyrroles. With this methodology, a variety of alkyl groups, which are primary, secondary, and tertiary as well as cyclic and functionalized types, can be introduced in place onto the pyrrole ring. The simplicity performable as a catalytic one-step process is one of the important features of this reaction. The substituent on the nitrogen atom of the product ?-alkylpyrrole can be removed easily by literature procedures. Therefore, the indium-catalyzed ?-alkylation plus the N-deprotection is a powerful system for all six variations, which are N-substituted and N-unsubstituted ?-alkylpyrroles having primary, secondary, and tertiary alkyl groups. Our method is applicable to synthesizing, albeit in two steps, ?-pyrrolyl-group-connected unsymmetrical tetraarylmethanes that have not been addressed thus far. Mechanistic studies showed the following three aspects: (1) dipyrrolylalkanes produced in situ from the pyrrole and carbonyl compound are key intermediates, (2) the selective ?-alkylation is attributed to the selective elimination of an ?-pyrrolyl group from the dipyrrolylalkane intermediates, and (3) the indium Lewis acid catalyst is indispensable for the progress of both stages.

Citation S. Nomiyama; T. Ogura; H. Ishida; K. Aoki; T. Tsuchimoto.Indium-Catalyzed Regioselective ?-Alkylation of Pyrroles with Carbonyl Compounds and Hydrosilanes and Its Application to Construction of a Quaternary Carbon Center with a ?-Pyrrolyl Group.. J Org Chem. 2017;82(10):51785197. doi:10.1021/acs.joc.7b00446

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