[3,3]SIGMATROPIC RING EXPANSION OF CYCLIC THIONOCARBONATES .13. SYNTHESIS OF MEDIUM-MEMBERED HETEROCYCLIC ALLENES AND SYNTHETIC APPLICATION TO ANTIFUNGAL CONSTITUENT OF SAPIUM-JAPONICUM

Cyclic allenes (3a-k, 3n) containing a SCOO moiety in the range of 8- to 11-membered ring were synthesized by the [3,3]sigmatropic rearrangement of the alkynyl cyclic thionocarbonates (2). Ring expansion of 6-membered cyclic thionocarbonates (2i-k) afforded a new type of strained 8-membered heterocyclic allenes (3i-k) in high yields. The MNDO optimized structure of 3i indicated the allenyl moiety was bent and strained. The reactivity of 8-membered cyclic allenes was also examined. Further, using this methodology with a novel application of a SmI2-HMPA reduction of the resulting heterocyclic allene (3n), an antifungal constituent of a Sapium japonicum, (+/-)-methyl 8-hydroxy-5,6-octadienoate (24), was synthesized.