Brønsted Acid‐Catalyzed Enantioselective Cycloisomerization of Arylalkynes.

The first example of an enantioselective carbocyclization of an alkyne‐containing substrate catalyzed by chiral Brønsted acids was achieved. The use of the 2‐hydroxynaphthyl substituent on the alkyne as a directing group constituted the key parameter enabling both efficient regioselective protonation of the carbon–carbon triple bond and chiral induction. The key cationic intermediate could be depicted either as a cationic vinylidene ortho‐quinone methide or a stabilized vinyl cation. Atropoisomeric phenanthrenes derivatives were produced in high yields and good enantioselectivities under mild, metal‐free reaction conditions in the presence of chiral N‐triflylphosphoramide catalysts. The carbenic nature of the cationic intermediate was also exploited to describe an example of alkyne/alkane cycloisomerization. [ABSTRACT FROM AUTHOR]