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
Bond angles at thiohydroxamate oxygen in crystal structures of 3-alkoxy-5-(p-methoxyphenyl)-4-methylthiazole-2(3H)-thiones gradually increased with the size of the 3-alkoxy substituent. This effect was attributed to strain on the basis of (i) a linear free energy relationship (Taft-Dubois correlation) and (H) signal coalescence from resonances of diastereotopic CH3 groups in solution (O-cumyl substituent; DNMR). Substitution at oxygen along the sequence OR (R prim-, sec-, and tert-alkyl), CH, and OLi was reflected in a gradual decrease of N,O distances and lengthening of associated C,S bonds. The responsivity for these changes was more pronounced in the thiazole-2(3H)-thione than in the pyridine-2(1H)-thione series. (C) 2009 Elsevier Ltd. All rights reserved.
Efficiency of alkoxyl radical product formation from 5-substituted 3-alkoxy-4-methylthiazole-2(3H)-thiones
In a comparative study, reactions between 5-(p-methoxyphenyl)-substituted 3-alkoxy-4-methylthiazole-2(3H)-thiones and appropriate mediators (BrCCl3, Bu3SnH) provided higher yields of alkoxyl radical products (δ-bromohydrins, cyclic ethers, carbonyl compounds) than respective transformations of 5-phenyl- and 5-methyl-substituted derivatives. The unusual selectivity of applied thiohydroxamates to furnish
<i>N</i>-Alkoxy-4-methyl-5-(<i>p</i>-anisyl)thiazole-2(3<i>H</i>)thiones - New Precursors for Visible Light- or Thermally-Induced Alkoxyl Radical Reactions in Synthesis
作者:Jens Hartung、Thomas Gottwald、Kristina Špehar
DOI:10.1055/s-2003-36794
日期:——
Visible light-initiated or thermally induced N-O homolysis of hitherto unknown 4-methyl-5-(p-anisyl)-substituted N-alkoxythiazolethiones furnishes alkoxyl radicals, which have been applied in the diastereoselective synthesis of bicyclic tetrahydrofuran rac-5 (5-exo-trig cyclization), formation of erythrose derivative 8 (β-C,C cleavage), and the preparation of bromoalcohol 10 (via selective 1,5-H-translocation)