Methyl carbenoid addition to enol ethers carrying a chiral auxiliary. Stereocontrol of three chiral centers on cyclopropyl ether
作者:Takashi Sugimura、Toshifumi Katagiri、Akira Tai
DOI:10.1016/s0040-4039(00)74133-5
日期:1992.1
Enolethers carrying an optically active 1,3-diol as a chiral auxiliary were subjected to cyclopropanation with methyl carbenoid. The chiral auxiliary well differentiated the prochirality of the reagent as well as the substrate.
Chiral and flexible 2,4-pentanediol-tethered cyclopropanation of olefins with a carbenoid derived from a diazo ester to construct three stereogenic centers
2,4-Pentanediol-tethered cyclopropanation of an olefin with an internal carbenoid generated from a diazo ester proceeded smoothly to give a chiral adduct having three stereogenic centers under full stereocontrol. The high stereoselectivity was not affected by the structure of the olefinic portion, studied so far with six substrates. Conversion of the product cyclopropane to other optically active compounds
An appropriate solvent to perform the original Simmons–Smith reaction was reinvestigated. Among available solvents, cyclopentyl methyl ether (CPME), a recently commercialized ethereal solvent, was found to be the best so far. Compared with Et2O under reflux – the commonest conditions – reaction completion in CPME at 50 °C was about 10 times faster. The product yields and selectivities were mostly identical
Stereospecificannulation of hydroxyvinylethers in the presence of triflic anhydride and tertiary amines and its syntheticapplication are described. Each 1-hydroxy-2-oxabicyclo[n.4.0]alkane, 2-oxabicyclo[n.4.0]alk-1(6)-ene and 2-oxabicyclo[n.4.0]alk-1(6+n)-ene is stereoselectively synthesized from the same hydroxyvinylether depending on the choice of the reaction conditions (temperature, solvent
描述了在三氟甲磺酸酐和叔胺存在下的羟基乙烯基醚的立体定向环氧化及其合成应用。每个1-羟基-2-氧杂双环[n.4.0]烷烃,2-氧杂双环[n.4.0] alk-1(6)-烯和2-氧杂双环[n.4.0] alk-1(6 + n)-烯根据反应条件(温度,溶剂和叔胺)的选择,由相同的羟基乙烯基醚立体选择性地合成。这些化合物导致多官能化的环状化合物和一些天然产物。我们提出,这种环化反应是通过纯S N 2样机理进行的。
Highly regio- and stereo-selective annulation–elimination reactions of 1-cycloalkenyl 3-hydroxypropyl ethers
Highly regio- and stereo-selective annulationâelimination reactions of 1-cycloalkenyl 3-hydroxypropyl ethers in the presence of triflic anhydride and tertiary amines are described; the bicyclic vinyl ethers produced are converted to 2-substituted δ-lactones, macrocyclic oxolactones and bicyclic hydroxy ethers by ozonolysis and stereoselective hydroboration.