Reusable, homogeneous water soluble photoredox catalyzed oxidative dehydrogenation of N-heterocycles in a biphasic system: application to the synthesis of biologically active natural products
the substrate and catalyst at room temperature. Its potential applications to organic transformations are demonstrated by the synthesis of various biologically active N-heterocycles such as indoles, (iso)quinolines and β-carbolines and natural products such as eudistominU, norharmane, and harmane and precursors to perlolyrine and flazin. Without isolation and purification, the catalyst solution can
Employing TBN/TEMPO as the catalysts and oxygen as the oxidant, the biologically and pharmaceutically significant tetrahydro-β-carboline and β-carboline alkaloid scaffolds that used to be obtained by multi-step processes can now be selectively obtained in only one-step via direct aerobicoxidative Pictet–Spengler reactions of tryptamines with alcoholsundermildconditions, with water generated as
Among all methods, aerobicoxidative aromatization is one of the most effective. However, in homogeneous conditions, catalysts are difficult to be recycled. Herein, we report a heterogeneous catalytic strategy with a mesoporous cobalt oxide as catalyst. The developed protocol shows a broad applicability for the synthesis of N-heterocycles (32 examples, up to 99 % yield), and the catalyst presents high turnover
DBN has been identified as an efficient reagent for promoting the dehydrogenative/decarboxylative aromatization of tetrahydro-β-carbolines under air atmosphere, to access the corresponding β-carbolines in moderate to good yields. The utility of this protocol for the gram-scale synthesis of β-carboline alkaloids eudistomin U (7) and harmane (10) has also been demonstrated.
o-Benzenedisulfonimide as a reusable acid catalyst for an easy, efficient, and green synthesis of tetrahydroisoquinolines and tetrahydro-β-carbolines through Pictet–Spengler reaction
tetrahydro-β-carbolines, using the Pictet–Spengler reaction, was carried out in the presence of a catalytic amount of o-benzenedisulfonimide, which worked as a Brønstedacid organocatalyst. The reaction conditions were mild and green and good target product yields were achieved. The catalyst was easily recovered and purified, ready to be used in further reactions with economic and ecological advantages.