Formation of 2,3-Dihydrothiophene-3-carboxylates from 2(5H)-Thiophenonesvia Sequential Cyclization and Ring-Opening Reactions of 3-Thiahexa-1,5-dienyl Radicals. Preliminary Communication
作者:Ren� Kiesewetter、Paul Margaretha
DOI:10.1002/hlca.19870700115
日期:1987.2.4
Methyl 4-mercapto-2-alkenoates 1, obtained by irradiation of 2(5H)-thiophenones 2 in MeOH, undergo light-induced S–H bond homolysis to give thio radicals 3 which can be trapped with 2-butyne to afford 3-thiahexa-1,5-dienyl radicals 12. Intermediates 12 undergo selective 1,5-ring closure to allylcarbinyl radicals 18, which cyclize to cyclopropylcarbinyl radicals 19. A novel rearrangement of 19 to 23
Mechanistic evidence for the light-induced ring opening of thiophen-2(5H)-ones 1 in alcohols affording α, β-unsaturated mercapto esters 2 is presented. Regio-and stereochemical aspects of the ring closure of alkenylthio (type 3) radicals 15 and 17 to S-heterocycles 16 and 18, of 3-thiahex-5-enyl radicals 4 to (tetrahydrothien-3-yl)methyl radicals 6 and of (2,3-dihydrothien-3-yl)methyl radicals 30 (type