Asymmetric construction of novel bicyclo[4.4.0] and [4.3.0]ring systems via intramolecular Horner–Wadsworth–Emmons reactions
摘要:
Novel perhydro-indanones and -naphthalenones having a quaternary stereogenic carbon and tetrasubstituted olefinic linkage were prepared via asymmetric intramolecular Horner-Wadsworth-Emmons reactions. The optically active binaphthyl phosphonates were connected with the 2-substituted cyclopenta- or cyclohexa-1,3-dione through the linker arm and the successive base treatment of the products with diethylzinc led to cyclization reactions with concomitant differentiation of diastereotopic carbonyl groups to afford the non-racemic title compounds in good enantiomeric excess. The absolute structure of the cyclized product was determined by X-ray analysis of its derived bromide. (C) 2002 Elsevier Science Ltd. All rights reserved.
Differentiation of enantiotopic carbonyl groups by the horner-wadsworth-emmons reaction
摘要:
A chiral phosphonoacetate 2 differentiates the enantiotopic carbonyl groups in an alpha-diketone 5 to afford the Z-olefin 6 in high yield and ee. The absolute stereochemistry of 6 was determined by X-ray analysis of 8 derived from 6.
Synthesis of the C(1)–C(16) fragment of bryostatins using an ‘ene’ reaction between an allylsilane and an alkynone
作者:Matthew O’Brien、Eric J. Thomas
DOI:10.1016/j.tet.2011.09.064
日期:2011.12
mediated ‘ene’ reaction between (4R)-4,5-bis-(tert-butyldimethylsilyloxy)-2-(trimethylsilylmethyl)pent-1-ene (43) and (5S,7R,9S)-5,11-dibenzyloxy-4,4-dimethyl-7,9-dihydroxy-7,9-O-isopropylideneundec-1-yn-3-one (53) gave the (E)-vinylsilane 54 with excellent stereoselectivity. Simultaneous deprotection and cyclisation via a stereoselective oxy-Michael reaction gave the bicyclicacetal 57 after treatment
The catalyticasymmetric total synthesis of (−)‐exiguolide, a complex 20‐membered macrolide embedded with a bis(tetrahydropyran) motif, is reported. The convergent synthesisinvolves the construction of the C1–C11 tetrahydropyran segment via catalyticasymmetric allylation and Prins cyclization, and the formation of the C12–C21 phosphonate segment via catalyticasymmetric cyclocondensation reaction
antitumor agents are currently in phase II clinical trials for the treatment of a variety of forms of cancer. Aldol reactions and directed reductions are among the essential steps for the formation of fragments A-C in the total synthesis of the title compound. Coupling of these fragments by sulfone-based olefination and alkylation reactions was followed by macrocyclization and introduction of the enoate moieties
作者:David A. Evans、Percy H. Carter、Erick M. Carreira、André B. Charette、Joëlle A. Prunet、Mark Lautens
DOI:10.1021/ja990860j
日期:1999.8.1
The total synthesis of the marine macrolide bryostatin 2 is described. The synthesis plan relies on aldol and directed reduction steps in order to construct the anti-1,3-diol array present in each of the principal subunits (A, B, and C). These fragments were coupled using a Juliaolefination and subsequent sulfone alkylation. A series of functionalization reactions provided a bryopyran seco acid, which
The totalsynthesis of bryostatin 9 was accomplished using a uniquely step-economical and convergent Prins-driven macrocyclization strategy. At 25 linear and 42 total steps, this is currently the most concise and convergent synthesis of a potent bryostatin.