Elucidation of the stereostructure of the annonaceous acetogenin (+)-montecristin through total synthesis
作者:Christian Harcken、Reinhard Brückner
DOI:10.1039/b002905j
日期:——
Total syntheses of ent-5-epi-montecristin (1a) and of (−)-montecristin (1b) were accomplished. The stereocenters of compounds 1a and 1b were established by asymmetric dihydroxylations of the trans-configurated β,γ-unsaturated esters 6 ( → 4, up to 80% ee; Scheme 3; improved procedure with up to 94% ee: Scheme 7) and 56 ( → 55, 97% ee: Scheme 9) while the stereogenic CC bonds stem from the carbocuprations
Enantiomeric β-angelica lactone epoxides: their syntheses from suitable chiral precursors and their use in the preparation of blastmycinone
作者:Rosa M. Ortuño、Daniel Alonso、Jaume Cardellach、Josep Font
DOI:10.1016/s0040-4020(01)86801-0
日期:1987.1
Syntheses of (S)-β-angelica lactone from L-tartaric acid and (R)-γ-hydroxy-methyl-γ-butyrolactone, 5, are reported. Alternative routes to prepare 5 from S- and R-glutamic acids and D-ribonolactone, respectively, are also presented. Epoxides derived from (R)- and (S)-β-angelica lactones have been obtained and their use in the synthesis of both (+)- and (-)-blastmycinone, 24, has been established.
dialkoxyboranes derived from thioesters were found to be stereoconvergent: both Z and E enolates give syn aldol condensation products. The thioester additions to chiral aldehydes were studied. Internal selectivity (syn) was usually very high, while the relative stereoselectivity ranged from poor to good, depending on the specific aldehyde used. The aldol products were transformed to known compounds for correlation
O-Methyloscillatoxin D and its analogues were concisely synthesized by a bioinspired intramolecular Mukaiyama aldol reaction as a key step, which involves the construction of a novel spiro-ether moiety.
A Four-Step Route from Aldehydes to C<sub>2</sub>-Elongated Enantiomerically Pure <i>α</i>,<i>β</i>-Unsaturated <i>γ</i>-Hydroxy Esters
作者:Christian Harcken、Reinhard Brückner
DOI:10.1055/s-2001-13372
日期:——
Asymmetric dihydroxylation of β,γ-unsaturated esters 4 provided β-hydroxy-γ-lactones 3 or ent-3. Methanolysis acetonide formation and LDA-mediated fragmentation of the resulting esters 5/ent-5 furnished the γ-chiral acrylates 6/ent-6 containing disubstituted C=C bonds (93-99% ee). Also, β-hydroxy-γ-lactones ent-3 a and 3 b were α-butylated and α-brominated, respectively, prior to methanolysis, acetonide formation, and fragmentation which led to the γ-chiral acrylates 9 and 12 with trisubstituted C=C bonds (94 and 95% ee, respectively).