Stereoselective Preparation of Ceramide and Its Skeleton Backbone Modified Analogues via Cyclic Thionocarbonate Intermediates Derived by Catalytic Asymmetric Dihydroxylation of α,β-Unsaturated Ester Precursors
作者:Linli He、Hoe-Sup Byun、Robert Bittman
DOI:10.1021/jo001226n
日期:2000.11.1
yields. Furthermore, propargylic alpha-azido-beta-hydroxyester 10a is converted to D-erythro-sphingosine 2a via simultaneous reduction of the triple bond, azido, and ester functional groups with LiAlH(4), providing a highly concise and practical four-step synthesis of this key naturallyoccurring sphingolipid. The L-erythro stereoisomers are also available in high enantiomeric purity by the method described
We have developed catalytic isomerizations of 5-alkynals to γ-alkynyl ketones and cyclopent-1-enylketones using [RhP(OPh)3}2]BF4 as a catalyst. Cu(OTf)2 and AgBF4 are also effective catalysts for the formation of γ-alkynyl ketones. The substituents at the 4-positions in 5-alkynals play important roles in the selection of two different isomerization pathways. The first catalytic endo/trans hydroacylation
The transition-metal-catalyzed rearrangement of 5-alkynals to γ-alkynylketones and 1-cyclopentenylketones was developed using [Rh(P(OPh)3)2]BF4 or Cu(OTf)2 as a catalyst.
novel intramolecularhydroacylation of 5- and 6-alkynals leading to alpha-alkylidenecycloalkanones was accomplished by using cationic a rhodium(I)/BINAP complex. For all cyclizations described, a single (E)-olefin isomer was obtained. At elevated temperature, hydroacylation and double bond migration of 5- and 6-alkynals proceeded in a one-pot reaction to give cycloalkenones. An intramolecular hydroacylation