Synthesis of the North 1 Unit of the Cephalostatin Family from Hecogenin Acetate
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- 作者：Seongkon Kim ; Scott C. Sutton ; Chuangxing Guo ; Thomas G. LaCour ; and P. L. Fuchs
- 刊名：Journal of the American Chemical Society
- 出版年：1999
- 出版时间：March 17, 1999
- 年：1999
- 卷：121
- 期：10
- 页码：2056 - 2070
- 全文大小：931K
- 年卷期：v.121,no.10(March 17, 1999)
- ISSN：1520-5126
文摘
Hecogenin acetate (1) was converted to North 1 azidoketone 5 involving several key transformations: (1) conversion of cyclic sulfate 33b to allylic alcohol 40 via Reich iodoso olefination; (2) E-ring annulationvia intermolecular oxygen alkylation of highly functionalized secondary alcohol 40 using rhodium-catalyzeddecomposition of an 
-diazophosphonoacetate to provide -alkoxyphosphonoacetate 52, with subsequentintramolecular Wadsworth-Emmons reaction to provide alkoxydihydrofuran 53; and (3) establishment of theC20 stereochemistry by chromium(II) reduction of tertiary bromide 86 to a 9:1 mixture of diastereomericspiroketals 90/90
, separated as silyl ethers 91/91. Conversion of 91 to -azidoketone 5 was uneventful.
-diazophosphonoacetate to provide -alkoxyphosphonoacetate 52, with subsequentintramolecular Wadsworth-Emmons reaction to provide alkoxydihydrofuran 53; and (3) establishment of theC20 stereochemistry by chromium(II) reduction of tertiary bromide 86 to a 9:1 mixture of diastereomericspiroketals 90/90, separated as silyl ethers 91/91. Conversion of 91 to -azidoketone 5 was uneventful.