Solid-Phase Synthesis of Pyrazolines and Isoxazolines with Sodium Benzenesulfinate as a Traceless Linker
作者:Yu Chen、Yulin Lam、Yee-Hing Lai
DOI:10.1021/ol0340888
日期:2003.4.1
text] The preparation of pyrazoline and isoxazoline derivatives with tracelesssolid-phase sulfone linker strategy is described. Key steps involved in the solid-phase synthetic procedure include (i) sulfinate S-alkylation, (ii) sulfone anion alkylation, (iii) gamma-hydroxy sulfone --> gamma-ketosulfone oxidation, and (iv) traceless product release via elimination-cyclization. A library of 12 pyrazolines
4-Substituted Hantzsch 1,4-dihydropyridines and 1,3,5-trisubstitutedpyrazolines were oxidized to the corresponding pyridines and pyrazoles, respectively, in high yields by molecular oxygen in the presence of catalytic amount of N-hydroxyphthalimide (NHPI) and Co(OAc)2 in acetonitrile at room temperature.
An unprecedented facile oxidation of 1,3,5-trisubstitutedpyrazolines and Hantzsch 1,4-dihydropyridines (DHPs) to the corresponding pyrazoles and pyridines was observed, mediated by 3,4-dihydro-2H-pyran in air. The reaction showed excellent reactivity, functional group tolerance, and high yield without using any metal and/or halogen based oxidizing agents.
Substrate Photoswitching for Rate Enhancement of a Organocatalytic Cyclization Reaction
作者:Matej Žabka、Ruth M. Gschwind
DOI:10.1002/ejoc.202200048
日期:2022.7.14
high catalyst loadings, as the processes are sluggish and complex equilibria are involved. Here, in situ light irradiation with a specific wavelength inside NMR is applied to increase reactionrates of hydrazone cyclization. This enhancement was achieved by isomerizing the substrate to the reactive configuration.