An unprecedented enantioselective synthesis of 3-substituted benzoxaboroles has been developed. An in situ generated ortho-boronic acid containing chalcone provides the chiral benzoxaboroles via an asymmetric oxa-Michael addition of hydroxyl group attached to the boronic acid triggered by the cinchona alkaloid based chiral amino-squaramide catalysts. In general, good yields with good to excellent enantioselectivities (up to 99%) were obtained. The resulting benzoxaboroles were converted to the corresponding chiral β-hydroxy ketones without affecting the enantioselectivity.
Bibliographical noteFunding Information:
This work has been funded by IISER Bhopal. GH and SM thank CSIR and UGC, New Delhi, India, respectively, for the doctoral fellowship. We are thankful to Dr Deepak Chopra, Associate Professor, IISER Bhopal for his useful suggestions. We are grateful to Mr Lalit M. Jha (IISER Bhopal) for X-ray crystallography.