10.1002/anie.201801340
Angewandte Chemie International Edition
COMMUNICATION
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treatment of 13ah with H2SO4 (Scheme 8b). The tosyl protecting
group could be easily removed in the presence of TBAF, leading
to the formation of free benzo[c]carbazole 15 in 95% yield.
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Scheme 8. Scope of Substituted Indole Synthesis and Derivatization.
In conclusion, we have developed highly efficient and
enantioselective propargylic substitution of azolium enolates and
acyl anions that are generated from aldehydes under NHC
catalysis without the need for transition metal activation. This
new catalytic activation triggers novel cascade cyclizations to
deliver skeletally diverse polycyclic compounds with good to
high efficiency and uniformly excellent enantioselectivity. Current
efforts in our laboratories are focused on the application of this
new catalytic activation to the preparation of other important
compounds in a stereoselective fashion.
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We are grateful for the generous financial support from A*STAR
SERC (R-143-000-648-305) and National University of
Singapore (R-143-000-605-221).
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Keywords: decarboxylation • cycloaddition • propargylic
substitution • heterocycle • enantioselectivity
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