Synthesis of Chiral 3H-Pyrrolo[1,2-a]indoles Via Organocatalytic Enantioselective Addition of Alkynyl Biphenyl Quinone Methides

An organocatalytic enantioselective reaction utilizing alpha-[4-(4-hydroxyphenyl)phenyl]propargyl alcohols and 3-substituted indoles has been successfully established for the synthesis of chiral 3H-pyrrolo[1,2-a]indoles. Through the assistance of an appropriate chiral phosphoric acid, a cascade sequence is facilitated, beginning with the dehydration of alpha-[4-(4-hydroxyphenyl)phenyl]propargyl alcohols to form alkynyl 4,4'-biphenyl quinone methides (4,4'-BQMs). Subsequently, 1,12-addition of 3H-pyrrolo[1,2-a]indoles to these alkynyl 4,4'-BQMs results in the formation of allenes, which are then protonated and regenerate 4,4'-BQMs. Finally, an enantioselective intramolecular annulation of 4,4'-BQMs occurs smoothly, leading to the production of a range of 3H-pyrrolo[1,2-a]indoles with high efficiency and asymmetric induction.