β-carbolines are substituted indoles that serve as the basic structures of common pharmaceutical drugs that have anti-cancer and neuroprotective properties. In 2019, Rajasekar and Anbarasan suggested a novel one-pot synthesis for dihydro-β-carbolines involving more than one catalytic system: a rhodium acetate dimer for C-H insertion on the indole and a basic organo-catalyst for the subsequent aza-Michael addition. Use of the chiral squaramide as the organo-catalyst affords excellent stereoselectivity. The proposed reaction mechanism has not been explored by either experimental or computational methods and identifying the rate-determining step would offer insight on how to improve reaction conditions, including lower reaction temperatures. The goal of this work is to determine the structure of all intermediates and transition states and calculate relative activation barriers using density functional theory (DFT) methods as implemented in the Gaussian suite of programs. We will model triethylamine, as well as squaramide, as the organo-catalyst, to explore the role of chirality in determining enantioselectivity.

Delineating the reaction energy profile of the enantioselective synthesis of dihydro-β-carbolines by tandem C-H activation and aza-Michael addition

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