Asymmetric Synthesis of Highly Functionalized 8-Oxabicyclo[3.2.1]octene Derivatives

Abstract

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 versatile intermediates in organic synthesis. The mechanism of the [3 + 4] annulation is considered to be a tandem cyclopropanation/Cope rearrangement. Such a mechanism is consistent with the excellent regio- and stereocontrol 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 (82−95% de) were obtained using 3-siloxy-2-diazo-3-butenoate derivatives as the vinylcarbenoid precursors.