THE 1,4-DITHIN RING-OPENING IN ISOTHIOQUINANTHRENE

The 1,4-dithiin ring opening reactions in isothioquinanthrene 1 (1,4-d ithiino[2,3-c;6,5-c']diquinoline) with selected S-, O- and Se-nucleoph iles in DMSO or DMF at 20-70 degrees C proceeded with cleavage of only one C-4-quinolinyl-S bond to give alkali metal salts of 4-substituted 4'-mercapto-3,3'diquinolinyl sulfides 2a-2h and 6 as primary products and after S-alkylation in aqueous sodium hydroxide solution 4-substit uted 4'-alkylthio-3,3'-diquinolinyl sulfides 3-5 and 7 as the final pr oducts. In contrast to sulfides 2a-2h sulfide 3a reacted with S-nucleo philes (sodium alkanethiolates) with cleavage of the C-3-quinolinyl-C- 4-quinolinyl-S and CH3-S bonds to form 3,4-dialkylthioquinolines 8a-8e as the main compounds. In the case of relatively bulky S-nucleophiles (the 2-methyl-2-propanethiolate and to some extent the ethanethiolate anions) the cleavage of the C-3-quinolinyl by a vicarious nucleophile (the methanethiolate anion, Liberated in the cleavage of the C-4-quin olinyl-S bond) was observed.