Bifunctional Borane Catalysis of a Hydride Transfer/Enantioselective [2+2] Cycloaddition Cascade

Abstract

Herein, we present am ild and efficient method for synthesizing enantioenriched tetrahydroquinoline-fused cyclobutenes through acascade reaction between 1,2-dihydroquinolines and alkynones with catalysis by chiral spiro-bicyclic bisboranes.T he bisboranes served two functions:f irst they catalyzedah ydride transfer to convert the 1,2-dihydroquinoline substrate to a1 ,4-dihydroquinoline,a nd then they activated the alkynone substrate for an enantioselective [2+ +2] cycloaddition reaction with the 1,4-dihydroquinoline generated in situ. Scheme 1. Enantioselective synthesis of cyclobutenes through [2+ +2] cycloadditionr eactions.

DFT study on stereoselective Rh-catalyzed intramolecular [2 + 2 + 2] cycloaddition of allene–ene–ynes

“…Transition metal catalysts can catalyze the construction of carbon rings and heterocycles in organic synthesis, 9 in which a cycloaddition strategy can provide a cycloalkane skeleton with several stereocenters in one reaction. 10 In the past few decades, many transition metals have been employed to catalyze cycloaddition reactions, such as Rh, Pd, Ru, Ni, Zn, Fe, Ir, Ag, Co, Au, Mn, and so on. 11 Rh transition metal catalysts have been used to catalyze cycloaddition reactions, for example, [4 + 2], 12 [3 + 2], 13 [5 + 1], 14 [2 + 2] 15 and [5 + 2] cycloaddition reactions.…”