Studies on the syntheses of hetrocyclic and natural compounds. part 948
作者:Tetsuji Kametani
DOI:10.1016/s0040-4020(01)98879-9
日期:1981.1
A simple method for the stereoselective synthesis of yohimbane (7) and alloyohimbane (5) via the diazoketone (2) from the anhydride (8), a symmetrical starting material, was examined. The preparation of pentacyclic ring systems contained in yohimbine and reserpine would be possible for the synthesis of such alkaloids by this method.
Symmetry-Driven Synthesis of Indole Alkaloids: Asymmetric Total Syntheses of (+)-Yohimbine, (-)-Yohimbone, (-)-Yohimbane, and (+)-Alloyohimbane
作者:Jeffrey Aube、Shomir Ghosh、Mehmet Tanol
DOI:10.1021/ja00099a019
日期:1994.10
Total asymmetric syntheses of the target alkaloids are reported. The syntheses involve the preparation of enantiomerically pure (S,S)-1,3,3a,4,7,7a-hexahydro-2(H)-inden-2-one 7 and its meso isomer 5. Each ketone is then converted into a ring-expanded lactam using an oxaziridine synthesis/rearrangement protocol. The applications of Bischler-Napieralski ring constructions along with appropriate functional group transformations afford enantiomerically enriched alloyohimbane or yohimbane from the meso- or C-2-symmetric ketones, respectively. A cis-5,6-diacetoxy compound (18) derived from the (S,S)-ketone served as the starting material for the total syntheses of the more highly functionalized alkaloids. Accordingly, a site-specific insertion of the indole-containing side chain was accomplished via stereoselective formation of an oxaziridine followed by its stereospecific rearrangement. The selectivity of this sequence allowed for the differentiation of alcohols at C-17 and C-18 (yohimbine numbering) and the synthesis of Delta 18,19-yohimbone. This alpha,beta-unsaturated ketone was converted into either (-)-yohimbone or (+)-yohimbine using standard chemistry.
A Chiral Pentenolide-Based Unified Strategy toward Dihydrocorynantheal, Dihydrocorynantheol, Protoemetine, Protoemetinol, and Yohimbane
作者:Changmin Xie、Jisheng Luo、Yan Zhang、Lili Zhu、Ran Hong
DOI:10.1021/acs.orglett.7b01573
日期:2017.7.7
An organocatalytic cross-aldol reaction of formaldehyde (formalin) with alkyl aldehydes, followed by the Z-selective Horner-Wadsworth-Emmons (HWE) reaction and immediate lactonization, afforded gamma-alkylated pentenolides in good overall yields and excellent enantioselectivities. Based on this scalable sequence, five quinolizidine alkaloids were synthesized in a unified and concise manner. The development of an in situ activation of a tertiary amide to improve the efficiency of the Bischler-Napieraiski (B-N) reaction was also noteworthy due to the generality to sensitive substrates for a variety of target molecules.
Corsano et al., Ricerca Scientifica, 1958, vol. 28, p. 2274,2275