10.1016/j.tetasy.2007.02.023
The research investigates the asymmetric Michael reaction to develop a method for synthesizing chiral b-ketophosphonates, which are valuable precursors for b-amino and b-hydroxy-phosphonates and have biological significance. The study focuses on using chiral b-enaminophosphonates derived from (S)-1-phenylethylamine and various electrophilic alkenes to achieve b,b-disubstituted ketophosphonates with high enantioselectivity and good yields. Key chemicals involved include the non-commercial b-ketophosphonate precursors 3a–3d, which were synthesized through a series of reactions involving hydrazones, Arbuzov reactions, and deprotection steps. The enaminophosphonates 4a–4d were then reacted with Michael acceptors such as phenylvinylsulfone and methyl acrylate. The study concludes that the asymmetric Michael reaction on acyclic enaminophosphonate compounds with non-substituted Michael acceptors is feasible, yielding chiral b-ketophosphonates with high enantiomeric excesses, similar to acyclic enaminoester derivatives. The introduction of dibenzyl- or diphenyl-phosphonate groups, however, decreased reactivity and enantioselectivity compared to diethylphosphonate groups. The absolute configurations of the adducts were determined using vibrational circular dichroism (VCD) due to challenges in obtaining single-crystal samples for X-ray analysis. Future work aims to extend this reaction to substituted Michael acceptors.
10.1016/S0040-4020(02)01518-1
The study focuses on the synthesis of 3-substituted-4-hydroxyquinoline N-oxides from Baylis–Hillman adducts derived from o-nitrobenzaldehydes. The key chemicals used in the study include trifluoroacetic acid, trifllic acid, and various Baylis–Hillman adducts such as 1b–f, which are derived from methyl vinyl ketone, phenyl vinyl sulfone, and ethyl acrylate. These chemicals serve the purpose of facilitating the reaction that yields the desired quinoline N-oxide derivatives. The study also explores the reaction mechanism, suggesting that N-hydroxyisoxazoline acts as a key intermediate in the process. The use of triflic acid was found to increase the acidity of the reaction medium, which was crucial for obtaining the quinoline N-oxides in reasonable yields. The study provides experimental evidence supporting the proposed reaction mechanism and successfully synthesizes several 3-substituted-4-hydroxyquinoline N-oxides, which are valuable synthetic intermediates.