Metal-catalyzed dehydrogenative synthesis of pyrroles and indoles from alcohols

This review is focused on the synthesis of various classes of pyrroles and indoles from alcohols as substrates or intermediates. Metal-induced dehydrogenation converts primary or secondary alcohols into the related carbonyl compounds (aldehydes or ketones), which can undergo in situ inter- or intramolecular attack by a carbon or nitrogen nucleophile to afford a new C-C or C-N bond, respectively. The formation of these bonds is the key step in the construction of the pyrrole and indole framework. Thus, pyrroles are obtained in good yields by dehydrogenative cyclization of beta-hydroxyenamines, and dehydrogenative N-heterocyclization of amines with diols, High yields of pyrroles are also obtained by reacting 2 amino alcohols with alcohols or ketones. Relevant is also the synthesis of pyrroles by a three-component reaction. Indoles are formed in high yields by intramolecular cyclization of 2-amino- and 2-nitrophenylethyl alcohols, and 2-aminobenzyl alcohols. Moreover, indole derivatives are also conveniently obtained by reaction of glycols or alcohols with anilines or phenyl hydrazine, respectively. (C) 2016 Elsevier B.V. All rights reserved.