Special Issue Reviews and Accounts ARKIVOC 2009 (i) 129-149
Ph H
OO O O
N N
H2SO4
(Eq. 2)
S S
S S
SS
S
SS
S
9
The N-(2-chloroethyl)diisopropylamine 10 constitutes a very special case. Its reaction with sulfur monochloride, whether or not in the presence of formic acid, gives the tricyclic bis[1,2]dithiolo[1,4]thiazine derivatives. The course of the reaction is completely changed by addition of phosphorus pentasulfide at the last stage of the reaction. In this case, the chlorine atom is replaced by sulfur both in the lateral chain or in the intermediate salt, thus giving a new [1,2]ditiolo[1,4]thiazine ring system.15 This new compound 11 has shown a notable antitumor activity against breast cancer cells at low concentration (10-4 M).
Cl
Cl
Cl S2Cl2
S2Cl2
OO
SS
N DABCO
DABCO
N
N
S
S
S
S
then HCO2H
then NEt3
S
S
S
S
S
S
10
N Cl N S S Cl S S Cl 2Cl Cl N S S S Cl S Cl S P4S10S2Cl2 S
S S
H
S
N
S S
S
SSS S SNCl P4S10
11
Scheme 5. Reaction of N-chloroethyldiisopropylamine 10 with S2Cl2.
The suggested mechanism for all these transformations involves as a key step transformation of isopropyl group into 3-chlorodithiolium salt 5. Going further with the investigation in this area, we demonstrated that the reaction can be stopped at the step of formation of monocyclic 1,2-dithioles.16 The main condition for the successful synthesis of monodithioles is low temperature (-15 °C). In agreement with the proposed mechanism the combination of an excess
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