Syntheses of (−)-gabosine A, (+)-4- epi-gabosine A, (−)-gabosine E, and (+)-4- epi-gabosine E

Abstract

(+)-4- epi-Gabosine A 1 and (−)-gabosine A 2 have been synthesized starting from methyl α, d-glucopyranoside and methyl α, d-mannopyranoside, respectively, by utilizing Pd(0) catalyzed Stille coupling as the key step. On the other hand, syntheses of (+)-4- epi-gabosine E 3 and (−)-gabosine E 4 have been accomplished from methyl α, d-glucopyranoside and from methyl α, d-mannopyranoside, respectively, by utilizing DMAP catalyzed Morita–Baylis–Hillman reaction as the key step. Presence of acetyl group at C-6 position of sugar derived cyclic enone prevented the aromatization of MBH adduct. A plausible mechanism is also described.