Abstract
A mild, efficient and environmentally benign method for synthesis of aromatic β-carbolines via Cu(ii)-catalyzed oxidation of 1,2,3,4-tetrahydro-β-carbolines (THβCs) was developed, in which air (O2) was used as the clean oxidant. This method has advantages such as environmentally friendliness, mildness, very good tolerance of functional groups, high yielding and easy experiment operation. In addition, this new methodology was successfully applied in the efficient and practical total syntheses of β-carboline alkaloids perlolyrine and flazin.
Highlights
The aromatic b-carboline skeleton is ubiquitous in many alkaloids,[1] bioactive congeners,[2] agrochemicals[3] and functional materials.[4]
In view of the signi cance of b-carbolines in drug discovery, agricultural chemistry and material science, development of practical, efficient and environmentally benign methods for syntheses of b-carbolines is of considerable interest and has attracted much attention from chemists.[5]
Amount of DBU has signi cant effect on the reaction (Entries 2 and 16–19), almost no desired product 2a could be obtained in the absence of DBU (Entry 16); and the reaction was hard to be complete even for a longer time, if less than 2.0 equivalents of DBU were used (Entries 17–19)
Summary
The aromatic b-carboline skeleton is ubiquitous in many alkaloids,[1] bioactive congeners,[2] agrochemicals[3] and functional materials.[4]. A possible mechanism for the CuBr2-catalyzed oxidative conversion of THbCs 1 to b-carbolines 2 is proposed in Scheme a Reaction conditions: THbCs 1 (2 mmol), CuBr2 (0.4 mmol), DBU (4 mmol), DMSO (6 mL), stirring at room temperature (25 C) under an atmosphere of air.
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