ABSTRACT
The stereoselective intramolecular dearomatizing spirocyclization of indoles via oxidative N-heterocyclic carbene (NHC) catalysis to afford indolenines bearing an all-carbon quaternary center at the 3-position is reported. The reaction proceeds via the intramolecular nucleophilic addition of the indole to an in situ generated α,ß-unsaturated acyl azolium. The cyclized indolenine bearing an acyl azolium functionality is trapped by a suitable external nucleophile that does not efficiently react with the α,ß-unsaturated acyl azolium via direct acylation.
ABSTRACT
An intramolecular dearomatizing spirocyclization of indoles by oxidative N-heterocyclic carbene catalysis is reported. C2-iodinated indoles are used as substrates in combination with aroyl azolium ions as acceptors, which provides C2-iodinated indolenines containing an all carbon quaternary stereocenter. The products are readily further C2-functionalized and give access to valuable oxindoles by simple hydrolysis in very good overall yields and excellent enantioselectivities.