Kinetic resolution of γ-iodo allylic alcohols by the Sharpless asymmetric epoxidation reaction proceeds with very large rate differences for the two enantiomers, thus providing a highly efficient method for preparation of optically pure . The alcohols thus prepared can be readily converted into various secondary allylic alcohols through the coupling reaction with nucleophiles.
Diastereoselective and Enantiospecific Synthesis of γ-Substituted α,β-Unsaturated Nitriles from O<i>-</i>Protected Allylic Cyanohydrins
作者:Alejandro Baeza、Jesús Casas、Carmen Nájera、José M. Sansano
DOI:10.1021/jo060239j
日期:2006.5.1
γ-Functionalized α,β-unsaturated nitriles are prepared diastereoselectively and enantiospecifically fromenantioenriched cyanohydrin-O-phosphates and carbonates derived fromα,β-unsaturatedaldehydes, either by palladium or iridium-catalyzed nucleophilic allylic substitution reactions with different nucleophiles. Appropriate reaction conditions for dibenzylamine, benzylamine, sodium azide, NaOAc,
A Facile Synthesis of Optically Active γ-Cyanoallylic Alcohols Using Asymmetric Hydrocyanation of α,β-Alkenyl Aldehydes Followed by Stereospecific [3.3]Sigmatropic Chirality Transfer of the Cyanohydrin Acetates
Optically active γ-cyanoallylic alcohols were synthesized by using asymmetric hydrocyanation of α,β-alkenyl aldehydes catalyzed by peptide-titanium complex to give α-cyanoallylic alcohols (cyanohydrins) with high optical yields followed by palladium complex catalyzed [3.3]sigmatropic chirality transfer of the corresponding acetates.
Binolam-AlCl: A Two-Centre Catalyst for the Synthesis of Enantioenriched CyanohydrinO-Phosphates
作者:Alejandro Baeza、Carmen Nájera、José M. Sansano、José M. Saá
DOI:10.1002/chem.200401290
日期:2005.6.20
The enantioselectivesynthesis of cyanohydrinO-phosphates by using in situ generated bifunctionalcatalysts (R)- or (S)-3,3'-bis(diethylaminomethyl)-1,1'-binaphthol-aluminium chloride (binolam-AlCl) is reported. The reaction, which can be described as an overall cyano-O-phosphorylation of aldehydes, has a wide scope and applicability. Evidence is also provided, including ab initio and DFT calculations
The addition of functionalized dialkylzincs to readily available beta-stannylated or beta-silylated unsaturated aldehydes in the presence of a catalytic amount of (1R,2R)-1,2-bis(trifluorosulfonamido)cyclohexane (8 mol%) provides chiral allylic alcohols in good yields (60-90%) and excellent enantioselectivity (usually in the range of 85-95% ee). The synthetic utility of these allylic alcohols as chiral building blacks is demonstrated. The gamma-stannylated allylic alcohols were submitted to a Stille coupling leading to polyfunctional allylic alcohols and gamma-alkoxy enones. A treatment with CuCN in N-methylpyrrolidone at 130 degrees C provided chiral unsaturated gamma-hydroxy nitriles. Finally, the desilylation of the gamma-silylated alcohols gave chiral allylic alcohols having a terminal double bond. The catalytic asymmetric addition was found to show an important inverse temperature dependance. A mechanism for this addition is proposed.