Two efficient and practical synthetic methodologies for the construction of small ring systems have been developed. The first method involves a novel rearrangement of cyclobutanes 10 and 14 leading to cyclopropanes 11 and 15 employing BF3.OEt(2) or POCl3 in the presence of pyridine or Raney nickel. The second method utilizes a novel cascade reaction of alpha,beta-unsaturated esters 25 and 36 possessing a cyclopropyl ketone moiety with TMSI in the presence of(TMS)(2)NH to afford polycyclic cyclobutane derivatives 26 and 38. A synthesis of(+/-)-anthoplalone (41) and a formal synthesis of (+/-)-lepidozene (42) were achieved utilizing 15, obtained by the above method.
Total Synthesis and Absolute Configuration of (−)-Anthoplalone
We report the total synthesis of the cytotoxic agent (-)-anthoplalone and the determination of its absolutestereochemistry. The cyclopropane moiety was prepared using a nonracemic bicyclic chloroallyl phosphonamide anion addition to tert-butyl 3,3-dimethyl acrylate. Several pathways were studied to secure the E-trisubstituted olefin of the left part of the molecule.