Stereoselective Construction of Fluorinated Quaternary Stereogenic Centers via an Organocatalytic Asymmetric <i>exo</i>-Selective Diels–Alder Reaction in the Presence of Water
作者:Bojan P. Bondzić、Konstantinos Daskalakis、Tohru Taniguchi、Kenji Monde、Yujiro Hayashi
DOI:10.1021/acs.orglett.2c03043
日期:2022.10.14
A catalytic, asymmetric Diels–Alderreaction of α-fluoro α,β-unsaturated aldehydes and cyclopentadiene was developed using diarylprolinol silyl ether as an organocatalyst. The reaction proceeds in toluene with trifluoroacetic acid as an additive (condition A). Perchloric acid salt of diarylprolinol silyl ether also promotes the reaction using water as a reaction medium (condition B). In both cases
Palladium-Catalyzed Stereoconvergent Formylation of (<i>E</i>/<i>Z</i>)-β-Bromo-β-fluorostyrenes: Straightforward Access to (<i>Z</i>)-α-Fluorocinnamic Aldehydes and (<i>Z</i>)-β-Fluorocinnamic Alcohols
We report here the stereoconvergent formylation of (E/Z)-beta-bromo-beta-fluorostyrene mixtures with carbon monoxide and sodium formate catalyzed by palladium. Optimization of reaction conditions leads to the corresponding pure (Z)-alpha-fluorocinnamaldehydes in good yields. The reaction was extended to styrenes bearing electro-attracting or electro-donating groups. The obtained alpha-fluoroaldehydes were smoothly reduced to the corresponding (Z)-beta-fluorocinnamic alcohol by NaBH4. The reaction could be performed on functionalized substrates as demonstrated by the access to the glucoside of beta-fluoroconiferyl alcohol, (Z)-beta-fluoroconiferin, a strong inhibitor of lignin polymerization.