Binaphthol-titanium-promoted, highly enantiocontrolled, Diels-Alder cycloadditions of electronically matched 2-pyrones and vinyl ethers: Streamlined asymmetric synthesis of an A-ring precursor to physiologically active 1α-hydroxyvitamin D3 ster

Article abstract of DOI:10.1016/S0040-4039(00)78338-9

Bicyclic lactones 4, A-ring precursors to diverse physiologically active 1α-hydroxyvitamin D₃ analogs, were prepared in excellent yields and enantiomeric purities via chiral, non-racemic Lewis acid-promoted, mild, inverse-electron-demand 4+2-cy