efficient synthesis from p-substituted acetophenones. Alkylation of heterocycles 6–10 in the form of their potassium or tetraalkylammonium salts 11–15 affords N-alkoxy-4-arylthiazole-2(3H)-thiones 16–20 in good to satisfactory yields. The hitherto unknown thiones 16–20 have been subjected to a detailed structural investigation (NMR spectroscopy and X-ray crystallography) and furthermore to a mechanistic
Towards Improved Alkoxyl Radical Precursors - The Synthesis of <i>N</i>-Alkoxy-4-(<i>p</i>-chlorophenyl)thiazole-2(3<i>H</i>)-thiones
作者:Jens Hartung、Michaela Schwarz
DOI:10.1055/s-1997-5754
日期:1997.7
4-(p-Chlorophenyl)-3-hydroxythiazole-2(3H)-thione (3) can be prepared in good yields and in useful quantities from p-chloro acetophenone (1). 0-Alkylation of the cyclic thiohydroxamic acid 3 via the respective potassium or the tetraethyl ammonium salts affords the esters 4. A slightly modified procedure allows the conversion of the acid 3 to the mixed anhydrides 5. The esters 4 and the anhydrides 5 are colorless to yellowish crystalline compounds which show a good shelf life. Visible light photolysis of the N-alkoxy derivatives 4e-g and reactive hydrogen donors affords substituted tetrahydrofurans 7 or tetrahydropyrans 8 via an alkoxyl radical pathway.
solvents affords alkoxylradicals, which were identified by (i) spin adduct formation (EPR-spectroscopy) and (ii) fingerprint-type selectivities in intramolecular additions (stereoselective synthesis of disubstituted tetrahydrofurans), beta-fragmentations (formation of carbonyl compounds), and C,H-activation of aliphatic subunits, by delta-selective hydrogen atom transfer. C-Radicals formed from oxygen-centered
Photoreactions of N-alkoxy-4-(p-chlorophenyl)thiazole-2(3H)-thiones with l-cysteine derivatives in aqueous solutions
作者:Jens Hartung、Rainer Kneuer、Kristina Špehar
DOI:10.1039/b101097m
日期:——
Photolysis of substituted N-alkoxythiazolethiones 1
in aqueous solvents furnishes alkoxyl radicals 2, which, upon
stereoselective 5-exo-trig cyclization, are trapped by water
soluble thiols (L-cysteine, L-cysteine ethyl ester,
or the reduced form of glutathione, GSH) to afford disubstituted
tetrahydrofurans 3 in synthetically useful yields and with satisfactory to
excellent diastereoselectivities.