Chemoselective 1,2- and 1,4-addition of malononitriles to ortho-formyl chalcones using cinchona alkaloid based bifunctional chiral organocatalysts has been shown by tuning the electronic nature of the malononitriles. Alkyl (hard) malononitriles undergo an asymmetric 1,2-addition followed by oxa-Michael reaction cascade to afford 1,3-disubstituted isobenzofurans with high enantio- and diastereoselectivity. Aryl (soft) malononitriles proceed through 1,4-addition followed by an aldol reaction cascade to provide indanols, having three consecutive stereocenters, in good yields and with good to excellent enantio- and diastereoselectivites.
Bibliographical noteFunding Information:
This work is funded by SERB (EMR/2016/005995), New Delhi, and IISER Bhopal. S.M. thanks UGC. M.S. thanks IISERB. G.H. thanks CSIR, New Delhi, India, for doctoral fellowships. We thank Mr. L.M. Jha, IISERB, for crystal data, and Dr. Mithu Saha for DFT calculation.
© 2017 American Chemical Society.