Highly diastereoselective Diels-Alder reactions with (R)-ethoxy p-tolyl vinyl sulfonium tetrafluoroborate

Article abstract of DOI:10.1016/S0957-4166(00)82159-X

p-Tolyl vinyl sulfoxide has been efficiently activated for the Diles-Alder reactions by transformation into a sulfonium salt 3a or by addition of TMSOTf.Very high diastereomeric excesses have been achieved (>98percent) at -20 deg C in many cases.Best results have been obtained with cyclopentadiene, furan and 2,3-dimethyl-1,3-butadiene.In this way enantiomerically pure oxanorbornenone 19a has been prepared.The reaction mechanism is briefly discussed.