Dearomative (3 + 2) Cycloadditions of Unprotected Indoles
Bram Ryckaert1, Jan Hullaert1, Kristof Van Hecke2
1Department of Organic and Macromolecular Chemistry, Ghent University, Krijgslaan 281-S4, B-9000 Ghent, Belgium.
Abstract:
The (3 + 2) cycloaddition of various indoles with a dithioallyl cation affords dearomatized cyclopentannulated adducts, with complete control of regioselectivity and excellent chemo- and diastereoselectivity. The success of the reaction critically relies on the use of an excess of very strong Brønsted acid, which paradoxically prevents carbocationic side reactions. The reaction tolerates sensitive functionalities such as basic amines or free hydroxyls, and we demonstrate its use in late stage derivatization of highly functionalized, unprotected indoles.
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