Wm. Choi et al., DEPENDENCE OF RING-OPENING REACTION OF 5-MEMBERED DITHIOCARBONATES ONCATIONIC CATALYST - CONTROL OF ISOMERIZATION AND POLYMERIZATION, Macromolecules, 31(8), 1998, pp. 2454-2460
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.