Regioselectivities of (4+3) Cycloadditions between Furans and Oxazolidinone-Substituted Oxyallyls

The (4 + 3) cycloadditions of oxazolidinone-substituted oxyallyls and unsymmetrically substituted furans lead to syn regioselectivity when the furan has a 2-Me or 2-COOR substituent, while anti regioselectivity is obtained with a 3-Me or 3-COOR group. OFT calculations are performed to explain the selectivities. The reactivities and regioselectivities are consistent with the ambiphilic reactivity of amino-oxyallyls with furans.