A Highly Enantioselective Approach to Hydrocarbazole Derivatives Catalyzed by Diphenylmethylidene Bis(oxazoline)‐Ni(II) Complexes

Abstract

The first Ni(II)-catalyzed asymmetric [4 + 2] cycloaddition of silyloxyvinylindoles with 2-enoyl pyridines was successfully accomplished by using a diphenylmethylidene-tethered bis (oxazoline). A series of optically active hydrocarbazole derivatives with three contiguous stereocenters were achieved in good yield with both high diastereo-(> 20 : 1) and enantioeselectivities (up to 97 % ee) under mild conditions. Moreover, various 2-enoyl azaarenes were compatible with the reaction. A proposed mechanism was deducted.

Squaramide-catalyzed enantioselective Michael addition of nitromethane to 2-enoylazaarenes: synthesis of chiral azaarene-containing γ-nitroketones

“…In recent decades, substantial focus has been directed towards the utilization of 2enoylpyridines and their N-oxides for a variety of asymmetric transformations. In particular, the enantioselective Michaeltype reactions catalyzed by organometallic complexes [8][9][10][11][12][13][14][15][16][17][18] and organocatalysts [19][20][21][22][23][24][25][26][27][28][29][30] have gained much more attention. Of the current catalytic systems, bifunctional chiral squaramides and (thio)ureas have emerged as undoubtedly the privileged catalysts for organocatalytic conjugate addition reactions between 2-enoylpyridines and various carbanion nucleophiles, including malononitrile, nitroalkanes, 1,3-dicarbonyl compounds, and so on (Scheme 1a).…”