Unusual Epimerization in Styryllactones: Synthesis of (−)-5-Hydroxygoniothalamin, (−)-5-Acetylgoniothalamin, and O-TBS-Goniopypyrone

[Image: see text] (−)-5-Hydroxygoniothalamin, (−)-5-acetylgoniothalamin, and (+)-5-hydroxygoniothalamin, isolated from the Goniothalamus genus, are synthesized from triacetyl-O-d-glucal by employing the Ferrier reaction, Mitsunobu reaction, and Jones oxidation as key steps. The synthetic procedure also yields the epimers of (−)-5-hydroxygoniothalamin and (+)-5-hydroxygoniothalamin employing acid-mediated transition-metal-free epimerization at C-5 of styryllactones. Further studies reveal that the epimerization is facilitated by the phenyl group present on the styryllactones. Also, depending on the dihydroxylation reaction conditions, various analogues of saturated styryllactones are synthesized utilizing oxa-Michael reaction conditions.