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Titanium-Catalyzed Intermolecular Hydroamination Route to Pyrroles
L. Ackermann*, R. Sandmann, L. T. Kaspar
Georg-August-Universität, Göttingen, Germany
22 June 2009 (online)
Based on previous results (L. Ackermann Synlett 2007, 507) two methodologies have been developed for the regioselective preparation of fully substituted pyrroles via titanium-catalyzed intermolecular hydroamination of a diastereoisomeric mixture of chloroenynes 2. This is the first report of such a pyrrole synthesis using a mixture of chloroenynes (E/Z)-2 for which an expected mechanism has been proposed. However, since derivatives 2 are often tedious to prepare, the use of the easily prepared α-haloalkynols 1 is an advantage of this method. The final pentasubstituted pyrroles are obtained via electrophilic aromatic substitution reactions within a one-pot protocol.