Substantial refinement of the photochemical synthesis of (+)-aspicillin

Article abstract of DOI:10.1016/0040-4039(91)80116-N

The photochemical synthesis of the 18-membered lichen macrolide (+)-aspicilin (1a), reported earlier, is characterized by the successful use of a photolactonization as a key reaction and by diastereoselective generation of stereogenic centers C(4), C(5), and (C(6). In comparison with an especially designed reference synthesis, where all the stereogenic centers came from the chiral pool, the photochemical synthesis of 1a needs further refinement. This has been achieved now by the use of ortho-formyl benzoic acid as a nucleophile in a Pd(0)-mediated epoxide ring opening furnishing an ester which is known easily to be hydrolyzed by morpholine catalysis.