Studies in sulfoxide rearrangement:: Regioselective synthesis of thieno[3,2-f]quinolin-7(6H)-one derivatives.

6-Mercapto-1-methylquinolin-2(1H)-one (3) was prepared in situ by the reductive cleavage of the corresponding disulfide 2 with Zn dust and acid. The disulfide 2 was in turn prepared via xanthate after diazotisation of 6-amino-1-methylquinolin-2-(1H)-one (1). 6-(4-Aryloxybut-2-ynylthio)-1-methylquinolin-2(1H)-ones (5a-e) were prepared from thiol 3 and 1-aryloxy-4-chlorobut-2-ynes (4). The sulfides 5a-e were then converted into the corresponding sulfoxides 6a-e by treatment with one equivalent of m-CPBA in CH2Cl2 at 0-5 degrees C for 30 min. The sulfoxides 6a-e were refluxed in CCl4 for 1 h to give the monothio-hemiacetals 7a-e in almost quantitative yields which were then converted into the 1-aryloxyacetyl-1,2-dihydro-6-methylthieno[3,2-f]quinolin-7(6H)-ones (11a-e) in almost quantitative yields by simply dissolving in absolute MeOH. Dehydrogenative elimination of product 11a-e when treated with acid generates 1-acetyl-6-methylthieno[3,2-f]quinolin-7(6H)-one (12) in 70-76% yield. (C) 1998 Elsevier Science Ltd. All rights reserved.