DEPENDENCE OF RING-OPENING REACTION OF 5-MEMBERED DITHIOCARBONATES ONCATIONIC CATALYST - CONTROL OF ISOMERIZATION AND POLYMERIZATION

The selective cationic isomerizations and ring-opening polymerizations of cyclic five-membered dithiocarbonates(la, 5-phenoxymethyl-1,3-oxat hiolane-2-thione; Ib, 5-methyl-1,3-oxathiolane-2-thione; Ic, 5-ethyl-1 ,3-oxathiolane-2-thione; Id, 5-chloromethyl-1,3-oxathiolane-2-thione) have been achieved by the selection of the catalysts, which have enabl ed the first facile preparations of 1,3-dithiolan-2-one derivatives (2 a-d) and polydithiocarbonates (P1a-d). The mechanism of the selectivit y was elucidated by the H-1 and C-13 NMR spectroscopic analyses for th eir reaction intermediates. The initiation steps of the reactions of l a with TfOEt or TfOH were different, wherein the formation of the cycl ic carbenium ion (6) via the ethylation of TfOEt on the thiocarbonyl s ulfur and the oxonium cation (7) via the protonation of TfOH on the et her oxygen were observed, respectively. The cation 7 might not be elec trophilic enough to be attacked by the monomer (1), which could explai n the fact that the results in the reaction of 1 selectively gave the isomer with TfOH. The polymerization and isomerization should proceed predominantly via 6 and 7, respectively. The reactivities of 1a-d decr eased in the order of Ib congruent to 1c > 1a > 1d, which showed good agreement with the H-1 NMR chemical shifts of the methine protons of 6 a-d.