Organocatalytic Enantioselective Synthesis of Tetrasubstituted α-Amino Allenoates by Dearomative γ-Addition of 2,3-Disubstituted Indoles to β,γ-Alkynyl-α-imino Esters

The first asymmetric synthesis of tetrasubstituted alpha-amino allenoates by a chiral phosphoric acid catalyzed dearomative gamma-addition reaction of 2,3-disubstituted indoles to beta,gamma-alkynyl-alpha-imino esters is reported. This method provides access to a series of highly functionalized tetrasubstituted allenes featuring quaternary stereocenters in high yields, and with excellent regio-, diastereo-, and enantioselectivities under mild conditions without by-product formation. Representative large-scale reactions and diverse transformations of the products into various scaffolds with potential biological activities render are also disclosed. The mechanism of the reaction was elucidated by control reactions and DFT calculations.