Diastereotopy in some 3,4-dihydroisocoumarins and related compounds

Some complex situations of diastereotopy involving two methylene groups abo ut a chiral centre are reported. In this regard, NMR data for protons at an d vicinal to the chiral centre in eight different 3,4-dihydrooisocoumarins (1), as well as eleven related compounds (2) are presented. In the dihydroi socoumarins (1) both methylene groups adjacent to the chiral centre behave as diastereotopes, except if the proton at this carbon is replaced by hydro xyl or methoxyl; in which case the ring methylene protons at C-4 exhibit on ly a singlet. On the contrary, the open-chain compounds, (2) exhibit diaste reotopy only for the methylene group directly bonded to the aromatic ring.