Medium to macrocyclic acetylenic lactones 15a-e 6-decyn-9-olide (15a), 7-undecyn-10-olide (15b), 8-dodecyn-11-olide (15c), 12-hexadecyn-15-olide (15d), and 5-decyn-9-olide (15e) were prepared from oxabicycloalkenones 7a-d and 2, respectively, by the ring expansion of their tosylhydrazones 16a-e, carried out by reaction with N-bromosuccinimide, under strictly controlled conditions. Complete hydrogenation (Pd-C, H2) of the triple bond gave the racemic saturated lactones: 9-decanolide (phoracantholide I, 6, from 15a and 15e), 10-undecanolide, 11-dodecanolide (dihydrorecifeiolide), and 15-hexadecanolide. The attempts at the conversion of dihydropyrones 7a,d into the respective acetylenic lactones 15a,d, via chlorohydrins 8a,d and/or chloroketolactones 9a,d, were only partially successful.
acetylenic lactones; chloroketolactones; chlorohydrins; ring expansion; tosylhydrazones; fragmentation reaction
