1. A General Route to β-Substituted Pyrroles by Transition-Metal Catalysis
- Author
-
Anon Bunrit, Svetlana Tsupova, Joseph S. M. Samec, Per J. R. Sjöberg, and Supaporn Sawadjoon
- Subjects
chemistry.chemical_classification ,Allylic rearrangement ,010405 organic chemistry ,Chemistry ,Aryl ,Organic Chemistry ,Aromatization ,010402 general chemistry ,Metathesis ,01 natural sciences ,Chloride ,0104 chemical sciences ,Catalysis ,chemistry.chemical_compound ,Yield (chemistry) ,medicine ,Organic chemistry ,Alkyl ,medicine.drug - Abstract
An atom-efficient route to pyrroles substituted in the β-position has been achieved in four high yielding steps by a combination of Pd, Ru, and Fe catalysis with only water and ethene as side-products. The reaction is general and gives pyrroles substituted in the β-position with linear and branched alkyl, benzyl, or aryl groups in overall good yields. The synthetic route includes a Pd-catalyzed monoallylation step of amines with substituted allylic alcohols that proceeds to yield the monoallylated products in moderate to excellent yields. In a second step, unsymmetrical diallylated aromatic amines are generated from the reaction of a second allylic alcohol with high selectivity in moderate to good yields by control of the reaction temperature. Ru-catalyzed ring-closing metathesis performed on the diallylated aromatic amines yields the pyrrolines substituted in the β-position in excellent yields. By addition of ferric chloride to the reaction mixture, a selective aromatization to yield the corresponding pyrroles substituted in the β-position was achieved. A reaction mechanism involving a palladium hydride, generated from insertion of palladium to O-H of an allyl alcohol, that is responsible for the C-O bond cleavage to generate the π-allyl intermediate is proposed.
- Published
- 2016