Brønsted Acid-Catalyzed Enantioselective Cycloisomerization of Arylalkynes
Julien Gicquiaud1, Baptiste Abadie1, Kalyan Dhara1
1CNRS, Bordeaux INP, ISM, UMR 5255, University of Bordeaux, 33400, Talence, France.
Abstract:
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.
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