Ls. Konstantinova et al., Synthesis of N-unsubstituted bis[1,2]dithiolo[1,4]thiazines and bis[1,2]dithiolopyrroles, J CHEM S P1, (20), 2000, pp. 3421-3427
The parent bis[1,2]dithiolo[1,4]thiazine-3,5-dione 8, -3,5-dithione 11, the
unsymmetrical 3-oxo-5-thione 10 and the bis[1,2]dithiolopyrrole-3,5-dione
9 are synthesised by acid catalysed cleavage of their various N-benzyl, eth
yl, ethoxycarbonylethyl and propanoic acid derivatives. These N-alkyl compo
unds are prepared in the usual way from the appropriate N-alkyldiisopropyla
mine and S2Cl2. N-Benzyl derivatives 2 and 5 of the thiazine and pyrrole di
ones give 8 (100%) and 9 (58%) respectively with conc. H2SO4 in dilute DCM
solution, and the N-ethyl thiazine derivatives of the dione 12 and the keto
-thione 13 give 8 (89%) and 10 (75%) respectively in conc. H2SO4 at 120 eps
ilon degrees C. Ethyl 3-(diisopropylamino)propanoate 16 with S2Cl2 gives th
e three thiazines 17 (30%), 18 (15%) and 19 (13%), and 17 and 19 are conver
ted into the pyrroles 20 (95%) and 21 (90%) respectively by thermal extrusi
on of sulfur in refluxing xylene. All five ethyl esters, 17-21, are hydroly
sed with aqueous acid to 22-26 respectively in 92-100% yield, and the N-pro
panoic acids 22-25 with hot conc. hydrochloric or hot 80-90% sulfuric acid
are dealkylated to the corresponding parent products 8-11. It is also shown
that the hydrolysis and dealkylation steps 17 --> 22 --> 8 can be combined
in one operation (75%).