Pectenotoxin-2 Synthetic Studies. 3. Assessment of the Capacity for Stereocontrolled Cyclization To Form the Entire C1−C26 Subunit Based upon the Double Bond Geometry Across C15-C16

Abstract

Second-generation synthetic routes to enantiopure sulfone 21 and aldehyde 24 are described. The union of these two intermediates by means of a Julia-Kocienski coupling gave rise to a series of E-configured building blocks that did not prove amenable to transannular cyclization. Alternatively, when the C15-C16 double bond was introduced with Z-geometry by Wittig olefination, spontaneous closure to generate a tetrahydrofuran culminated an ensuing direct dihydroxylation step. The structural assignment to 35, undergirded by detailed 1H and 13C NMR studies, is consistent with proper transannular bonding so as to deliver the entire C1-C26 fragment of PTX2.

A Stereoselective Synthesis of the C(13)-C(23) Fragment of Iriomoteolide-1b

“…在臭氧化反应中, 往反应体系加入硼氢化钠可 以一锅得到 13b, [10] 接着发生 Mitsnobu 反应和氧化反应 得 到 化 合 物 6. 在 我 们 尝试 了 很 多 条 件 后 发 现 , 在 DME/THF (V ∶ V ＝ 1 ∶ 1) 混 合 溶 剂 中 进 行 Julia-Kocienski [11] 反应可以得到较好的结果, 但是确定不了形成 的双键的构型, 我们将化合物 3 进行 DIBAL-H 还原得 到 E-4 [12] , 得到的双键构型单一. 至此, 我们完成了 Iriomoteolide-1b 中 C(13)-C(23)片段的立体选择性合成.…”