A convergent synthesis of the C(11)–C(25) fragment of the aglycone of avermectin A2b
摘要:
Oxidation of the mixture of products obtained by treatment of (S)-2-methylbutanal 8 with the E-but-2-enyldi-isopinocampheylborane prepared from (+)-pinene gave a mixture of homoallylic alcohols from which the major isomer 9 was isolated by chromatography. Oxidation with vanadylacetoacetate and tert-butyl hydroperoxide gave the epoxides 12 and 13, ratio 80 : 20. Following procedures developed in a synthesis of the model spiroacetal 19, 1,3-dithiane was alkylated, firstly using the epoxide 12, and then, after protection of the product 21 so obtained as its acetonide 23, using the epoxide 25, to give the 2,2-dialkylated 1,3-dithiane 25. Deprotection was accompanied by cyclisation to give the spiroacetal 28. Spiroacetal 29 was similarly prepared and taken through to the C(11)-C(25) fragment 38 of the aglycone of avermectin A(2b) 3. (C) 1997 Elsevier Science Ltd.
Asymmetric synthesis of milbemycin and avermectin spiroacetals
作者:Eric Merifield、Patrick G. Steel、Eric J. Thomas
DOI:10.1039/c39870001826
日期:——
Spiroacetals (16) and (29) have been synthesized from dimethyl (S)-malate (9)via convergent routes which use chiral boron reagents to control stereochemistry.
Total Synthesis of the Antiparasitic Agent Avermectin B1a
作者:James D. White、Gary L. Bolton、Anura P. Dantanarayana、Christina M. J. Fox、Roger N. Hiner、Randy W. Jackson、Kazuhiko Sakuma、Ulhas S. Warrier
DOI:10.1021/ja00112a006
日期:1995.2
The synthesis of avermectin B-1a has been completed by a route that assembles the aglycon from three subunits consisting of the hexahydrobenzofuran moiety (A), the spiroketal segment (B), and the acyclic portion (C) comprising C9-C15. Connection is made in a B + C --> (B - C) + A sequence, and the synthesis is concluded by attachment to the aglycon of the L-oleandrosyl-L-oleandrose disaccharide via the pyridylthio glycoside.