Taxane diterpenes 4: Autoxidation, epimerization and isomerization for the introduction of functionality into the taxane ABC ring system
摘要:
The bicyclo[5.4.0]undecenone 4 was converted through a four step sequence involving activation, gem-methylcyclopropanation and reductive cleavage into 18 alpha/beta, containing the B/C rings of the taxanes. The A-ring has been attached to the B/C ring system by cyclization of the sulfone-ester 23 alpha to give 24. The A-ring was modified to give 29, which underwent beta-elimination of the 3,10-oxido bridge via a dianion, followed by transannular hydride shift to give the butenolide 30 and 32. Autoxidation of 30 gave 33 which was further elaborated into the trans-fused B/C adduct 35. The isomeric 3,10-diones trans-39 and cis-45 undergo autoxidation using t-BuOK/THF/O-2/P(OEt)(3) to give 2 and 46 respectively without B/C cis/trans isomerization. (C) 1998 Elsevier Science Ltd. All rights reserved.
Isomerization, autoxidation and epimerization for the introduction of C-1 to C-5 functionality into the taxane ABC ring system
摘要:
Treatment of 2-ketotax-3-enes with r-BuOK/t-BuOH/THF/65 degrees C results in isomerization of the double bond into the 4,5-position and a trans-B/C ring fusion. Subsequent exposure to t-BuOK/THF/O-2/P(OEt)(3) introduces the C-1-hydroxyl group. Copyright (C) 1996 Elsevier Science Ltd