ASYMMETRIC-SYNTHESIS OF HIGHLY FUNCTIONALIZED 8-OXABICYCLO[3.2.1]OCTENE DERIVATIVES

Rhodium(II) carboxylate catalyzed decomposition of vinyldiazomethanes in the presence of furans results in a general synthesis of oxabicyclo [3.2.1]octa-2,6-diene derivatives. These oxabicyclic products are vers atile intermediates in organic synthesis. The mechanism of the [3 + 4] annulation is considered to be a tandem cyclopropanation/Cope rearran gement. Such a mechanism is consistent with the excellent regio- and s tereocontrol that is observed in these [3 + 4] annulations. Asymmetric synthesis of the oxabicyclic products is possible through utilization of rhodium(II) (S)-N-(tert-butylbenzene)sulfonylprolinate as catalyst or by using (S)-lactate or (R)-pantolactone as chiral auxiliaries on the carbenoid. The highest yields (69-95%) and asymmetric induction (8 2-95% de) were obtained using 3-siloxy-2-diazo-3-butenoate derivatives as the vinylcarbenoid precursors.