Palladium-copper catalyzed synthesis of benzofused heterocycles with two heteroatoms: novel and highly regio- and stereoselective syntheses of (E)-2-(2-arylvinyl)-3-tosyl-2,3-dihydro-1,3-benzothiazoles and (E)-2-alkyl(aryl)idene-3,4-dihydro-2H-1,4-benzothiazines.
A highly novel, general, and convenient palladium and copper-catalyzed procedure has been developed for the synthesis of (E)-2-(2-arylvinyl)-3-tosyl-2,3-dihydro-1,3-benzothiazoles 28-40. 3-(2-Aminophenylthio)prop-1-yne 1 reacts with aryl iodides 2-14 under palladium-copper catalysis to yield the disubstituted alkynes 15-27 which after tosylation undergo a novel cyclization with CuI in the presence of triethylamine in THF to (E)-2-(2-arylvinyl)-3-tosyl-2,3-dihydro-1,3-benzothiazoles 28-40 rather than to the expected 3-alkylidene-4-tosyl-3,4-dihydro-2H-1,4-benzothiazines 41. The reaction is highly regio- and stereoselective. The synthesis of 2-(2-arylethyl)-3-tosylbenzothiazolines 42-47, 2-(2-arylvinyl)benzothiazoles 48-54, and a novel 5-substituted uracil derivative 55 of potential biological importance is also being reported. Similarly, the palladium-copper-catalyzed arylation of S-[2-(N-prop-2'-ynyl)aminophenyl]-N,N-dimethylthiocarbamate 58 with aryl iodides yields the disubstituted alkynes 59 which on cyclization with KOH in methanol leads to (E)-2-(2-aryl)methylidene-3,4-dihydro-2H-1,4-benzothiazines 61. The reaction of the diiodo compounds 12-14a, however, with 58 under palladium-copper-catalyzed reactions involves the participation of only one of the iodo groups in the heteroannulation process giving compounds 61i and 61j. These are amenable to further palladium-catalyzed reactions and afford polyunsaturated heteroaromatic compounds 62 and 63.
Kundu
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NG
Department of Organic Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Calcutta-700 032, India. ocngk@mahendra.iacs.res.in
Nandi
B
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