Organocatalytic Enantioselective Synthesis of Axially Chiral Tetrasubstituted Allenes via Direct 1,8-Addition to <i>In Situ</i> Formed Alkynyl 8-Methylenenaphthalen-2(8 <i>H</i> )-ones

Organocatalytic enantioselective construction of axially chiral tetrasubstituted allenes has been achieved from the reaction between α-(2-hydroxynaphthalen-8-yl)propargylic alcohols and 2-arylindoles for the first time. With the aid of a suitable chiral phosphoric acid, alkynyl 8-methylenenaphthalen-2(8<i>H</i>)-one was formed <i>in situ</i> from the corresponding α-(2-hydroxynaphthalen-8-yl)propargylic alcohol, followed by enantioselective 1,8-conjugate addition of 2-arylindole to afford the target axially chiral tetrasubstituted allenes in 70-95% yields with 64-94% ee. Notably, this work establishes the 2-hydroxynaphthalen-8-yl unit as an effective auxiliary group that enables the corresponding α-functionalized propargylic alcohols for the construction of enantioenriched tetrasubstituted allenes, which enrich the chemistry of quinone methides.