A novel thermolytic annulation of an oxazolidinone: an enantiospecific synthesis of (-)-slaframine
摘要:
Optically pure beta-aminopiperidines can be prepared in high yields through a thermolytic annulation sequence involving ring opening of an oxazolidinone.
Synthesis of indolidines by the 1,3-dipolar cycloaddition of azides with methylenecyclopropanes followed by cyclopropyumine rearrangement
作者:Philip C. Heidt.‡、Stephen C. Bergmeier†、WilliAm H. Pearson‡
DOI:10.1016/s0040-4039(00)97867-5
日期:1990.1
Cyclic imines 6a and 6b were obtained by the intramolecular 1,3-dipolar cycloaddition of azides with methylenecyclopropanes. Acid catalyzed rearrangement produced bicyclic (−)-enamines 7, which upon reduction provided indoilizidenes 8. A similar strategy was used for the synthesis of (−)-8a-epi-desacctoxyslaframine 16.
Synthesis of (-)-slaframine and related indolizidines
作者:William H. Pearson、Stephen C. Bergmeier、John P. Williams
DOI:10.1021/jo00040a045
日期:1992.7
An enantioselective synthesis of the indolizidine alkaloid (-)-slaframine 1 is reported. Reductive double cyclization of the azido epoxy tosylate 48 afforded the indolizidine 52, which was converted to (-)-slaframine in two steps. The cyclization substrate 48 was prepared in optically pure form from L-glutamic acid. A similar sequence starting with the epoxide 49 allowed the synthesis of (-)-1,8a-diepislaframine 56. Other routes to slaframine were investigated, often using an intramolecular cycloaddition of an azide with an alkene as a key step. Although these routes did not produce slaframine, they illustrated novel and efficient methods for the assembly of the indolizidine skeleton. Cyclization of the azidodiene 20 afforded the indolizidine 21 in one step as a single diastereomer, presumably a result of a chairlike transition state in the initial dipolar cycloaddition. Desulfurization and deprotection produced (-)-8a-epidesacetoxyslaframine 27. Cyclopropylimine rearrangement of 30 gave the indolizidine 31, which was also converted into (-)-8a-epidesacetoxyslaframine 27. Dipolar cycloaddition of 38 gave the 1-pyrroline 39, which was converted to the indolizidine 40 in one operation using Evans' double alkylation of the 1-metalloenamine derivative of 40. Attempted oxidation of 40 to the ketone 41 was unsuccessful, precluding a reductive amination approach to slaframine.
A novel thermolytic annulation of an oxazolidinone: an enantiospecific synthesis of (-)-slaframine
作者:Mukund P. Sibi、James W. Christensen、Biqin Li、Paul A. Renhowe
DOI:10.1021/jo00042a002
日期:1992.7
Optically pure beta-aminopiperidines can be prepared in high yields through a thermolytic annulation sequence involving ring opening of an oxazolidinone.
HEIDT, PHILIP C.;BERGMEIER, STEPHEN C.;PEARSON, WILLIAM H., TETRAHEDRON LETT., 31,(1990) N8, C. 5441-5444
作者:HEIDT, PHILIP C.、BERGMEIER, STEPHEN C.、PEARSON, WILLIAM H.
DOI:——
日期:——
Enantiospecific Synthesis of (−)-Slaframine and Related Hydroxylated Indolizidines. Utilization of a Nucleophilic Alaninol Synthon Derived from Serine<sup>1</sup>
作者:Mukund P. Sibi、James W. Christensen
DOI:10.1021/jo9908546
日期:1999.8.1
A general methodology for the synthesis of indolizidine alkaloids delta-coniceine (12), 1-hydroxyindolizidine (20), desacetoxy slaframine (24), slaframine (34), and an analogue (37) has been developed. This convergent approach utilizes the available chirality in proline and serine and is conceptually different from other approaches. A highly stereoselective coupling of the prolinals with a nucleophilic alaninol synthon provides the precursors for the key cyclization. A novel thermolytic annulation of an oxazolidinone is the key step in the formation of the six-membered piperidine ring. Further elaboration provides the target natural products 24, 34, and 37 in good overall yields.