Diastereoselective synthesis of benzofuran-3(2H)-one-hydantoin dyads

A convenient diastereoselective rearrangement of the racemic (R/S)-spiro[chroman-2,4′-imidazolidine]-2′,4,5′-triones 3a–c into (2′R,5S)- and (2′S,5R)-5-(3-oxo-2,3-dihydrobenzofuran-2-yl)imidazolidine-2,4-diones 4a–c under alkali conditions is described. The obtained σ bridged benzofuran-3(2H)-one-hydantoin dyads 4a–c are subsequently transformed into π conjugated benzofuran-3(2H)-one-hydantoin dyads 5a–c by a diastereoselective dehydrogenation using I2 (catalytic)/DMSO system to predominantly yield the (Z)-isomer. The novel single and double bonded benzofuran-3(2H)-one-hydantoin conjugate structures 4a–c and 5a–c were unambiguously elucidated by single-crystal X-ray diffraction and 2D NMR techniques allowing an in-depth stereochemical and mechanistic discussions.