The Dual Role of Ruthenium and Alkali Base Catalysts in Enabling a Conceptually New Shortcut to N-Unsubstituted Pyrroles through Unmasked α-Amino Aldehydes
Kazuki Iida, Takashi Miura, Junki Ando and Susumu Saito*
*Graduate School of Science, Nagoya University, Chikusa, Nagoya 464-8602, Japan, and Institute for Advanced Research, Nagoya University, Chikusa, Nagoya 464-8601, Japan, Email: saito.susumuf.mbox.nagoya-u.ac.jp
K. Iida, T. Miura, J. Ando, S. Saito, Org. Lett., 2013, 15, 1436-1439.
DOI: 10.1021/ol4001262 (free Supporting Information)
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The dual effects of a catalytic ruthenium complex and an alkali metal base enable a virtually salt-free and straightforward bimolecular assembly giving N-unsubstituted pyrroles through fully unmasked α-amino aldehydes. Either solvent-free or acceptorless dehydrogenation achieve high atom step and pot economy by avoiding multistep operations involving protection/deprotection.
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If the Rf value (TLC) of the remaining ketone overlapped with that of the pyrrole, we reduced the ketone with 5 eq. NaBH4 in MeOH in aprox. 1 h to the corresponding alcohol to facilitate separation of the pyrrole.
Susumu Saito, May 1, 2014