Sigmatropic Ring Expansion of Cyclic Thionocarbonates. 13. Synthesis of Medium-Membered Heterocyclic Allenes and Synthetic Application to Antifungal Constituent of Sapium Japonicum

Article abstract of DOI:10.1016/0040-4020(95)00306-S

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 resulting heterocyclic allene (3n), an antifungal constituent of a Sapium japonicum, (+/-)-methyl 8-hydroxy-5,6-octadienoate (24), was synthesized.