The Intramolecular Die&Alder reactions of the dienynes readily obtainable from the aromatic aldehydes and ethyl 1-acetylcyclopentane-1-carboxylate, were found to proceed in a highly regioselective manner with formation of the novel title compounds as sole products. Fredericamycin A (1) has been distinguished as an unusually attractive target for total synthesis because of its prominent anticancer activity and characteristic Spiro structure.1) While the initial structural elucidation of 1 reported by Pandey et al. had only concerned with its relative configuration, lb) it was recently uncovered that 1 could be produced by Streptomyces species in an optically active form.21 However, the absolute stereochemistry of naturally occurring 1 has not been determined. Numerous synthetic approaches to 1 have hitherto been reported3) and Kelly et al. has recently completed the Fast total synthesis of 1 in a racemic modification by employing elegant synthetic methodology.4) We became interested in the unique s!mctnre of 1 involving a single chiral center at the Spiro junction of the CD-ring system, and started the program directed at the total synthesis of optically active 1 of definite absolute configuration.
However, all the synthetic methods so far developed, 3a-g5-kn,p,q74) turned out to be not applicable to this