Palladium(II)-catalyzed enyne cyclization strategies toward the podophyllotoxin ring system
作者:Jason N. Abrams、Qi Zhao、Ion Ghiviriga、Minaruzzaman
DOI:10.1016/j.tet.2011.11.002
日期:2012.1
the ABCD ringsystem of podophyllotoxin, but substitutes a D-ring furan for the D-ring lactone. Application of the recent methodology of Lu et al. (J. Org. Chem. 1995, 60, 1160–1169) on a related 1,6-enyne substrate led to functionalized α-methylene γ-butyrolactones instead (Pd2(dba)3·CHCl3, LiBr, and CuBr2). The latter conditions applied to an alkynoic alkene afforded the ABCD ringsystem of podophyllotoxin
bond scission with conjunctive cross‐couplings, this decarboxylative reorganization reaction features fascinating atom and step economy and provides an efficientapproach to highlyfunctionalized dienynes from readily available substrates. Without further optimization, gram‐scale products can be easily obtained by such a simple, neutral, and low‐cost catalytic system with high TONs. DFT calculations
A novel asymmetric catalysis via a palladium(II)/palladium(IV) cycle has been developed by utilizing a chiral spiro bis(isoxazoline) ligand (SPRIX). Intramolecular chlorinative cyclization of 1,6‐enynescatalyzed by a palladium‐SPRIX complex proceeded enantioselectively to afford α‐methylene‐γ‐lactone derivatives.
A method for the synthesis of allyl substituted γ-butenolides via carbonylylide rearrangement of vinyl sulfoxonium ylide-derived carbenes has been developed. At rt, the mechanism involves a carbonylylidegeneration/allyloxy furan formation/[3,3]-sigmatropic rearrangement/isomerization sequence for the generation of 3-allyl butenolides. At 70 °C, instead of the final isomerization step, the resulting