Highly Enantioselective Conjugate Addition of AlMe3 to Linear Aliphatic Enones by a Designed Catalyst
作者:Paul K. Fraser、Simon Woodward
DOI:10.1002/chem.200390087
日期:2003.2.3
of AlMe(3) to linear aliphatic enones in THF at -40 to -48 degrees C in the presence of [Cu(MeCN)(4)]BF(4). At ligand loadings of 5-20 mol %, enantioselectivities of 80-93 % are realised for most substrates. To attain these values, the use of highly pure AlMe(3) is mandatory. The presence of methylalumoxane (MAO), derived by hydrolysis, leads to reduced enantioselectivity and a conjugate addition product
Free radical-promoted, one-carbon, ring expansion of twelve, fourteen-, and fifteen-membered cyclic β-keto esters is described. The method is then extended to include a three-carbon ring expansion of cyclododecanone, the targets being (±)-muscone and naturally occurring (R)-(−)muscone.
(R)-(–)-Muscone was synthesized in a stereocontrolled manner via the diastereoselective conjugateaddition to a cyclic α,β-unsaturatedester of (R,R)-cyclohexane-1,2-diol accompanied by spontaneous Dieckmanncondensation.
configuration of the chiral ligand used. Thus the conjugate addition using the ligand prepared from exo-3-monosubstituted-amino-exo-2-hydroxybornane gave (S)-(+)-muscone, while with endo-ligand, (R)-(–)-muscone was obtained in higher enantioselectivity. Muscone of essentially 100% optical purity was obtained by the addition of small amounts of THF (tetrahydro-furan)(2–10 equiv.) to the toluene solution