Sultines as o-Quinodimethane Precursors in an Oxa-Diels-Alder Reaction: Synthesis of Functionalized Isochromans

The development of an oxa-Diels-Alder reaction between sultines and carbonyl compounds is reported. o-Quinodimethanes, generated from sultines, undergo a [4+2]-cycloaddition with activated aldehydes or ketones in the presence of Cu(OTf)(2) to provide a variety of functionalized isochromans, including spiroisochromans, in up to 99%yield. The developed protocol demonstrates broad functional-group compatibility and tolerates unprotected isatins bearing free NH-functionalities.