Sulfur Chemistry
It is ‘thiazolidine-2,4-dione’ and not thiohydantoins as the reaction product of monosubstituted thioureas and chloroacetylchloride a
a
a
a
a
The reaction products of monosubstituted phenylthioureas with chloroacetylchloride in a polyethylene glycol (PEG-400) medium and K2 CO3 as base/catalyst at an elevated temperature are exclusively thiazolidine-2,4-diones and not thiohydantoins as has been reported. The core unit thiazolidine-2,4-dione is essentially derived from chloroacetylchloride and the thioamidic part of the phenylthiourea. The scope of this unprecedented transformation has been evaluated with electron-rich and electron-poor phenylthioureas.
O
O
O
H
N
S
N
Cl
Cl
K2CO3 (5 mol %)
PEG-400, 80 oC
X
Cl
S
X
H
N
Cl
O
N
H
NH2 K2CO3 (5 mol %)
PEG-400, 80 oC
H2O
O
+ X
NH2
S
Keywords: monosubstituted thiourea; chloroacetylchloride; PEG-400; thiazolidine-2,4-dione
1.
Introduction
The mechanism of thiazole-2-imine formation has not been well understood leading to the proposal of incorrect structures for the products obtained by the reaction of thiourea analogs with αhaloketones by two independent research groups (1). Based on the principle of hard–soft reactivity,
i.e. hard nucleophile attacks on hard electrophile and the soft nucleophile on soft electrophile, we have suggested an alternative reaction mechanism for the formation of thiazole-2-imine. Our mechanism is supported by isolating the reaction intermediate, confirming its structure and that of the products by X-ray crystallography (2). Having understood the reactivity of thioureas toward α-haloketones, recently, we have suggested an alternative structure for the product obtained by the reaction of thiourea with chloroacetylchloride (3). The structure of the product is found to
have the 2-imino-4-thiazolidinones moiety (3) and not the thiohydantoin as has been reported previously by another group (4).
a
a
a
a
The reaction products of monosubstituted phenylthioureas with chloroacetylchloride in a polyethylene glycol (PEG-400) medium and K2 CO3 as base/catalyst at an elevated temperature are exclusively thiazolidine-2,4-diones and not thiohydantoins as has been reported. The core unit thiazolidine-2,4-dione is essentially derived from chloroacetylchloride and the thioamidic part of the phenylthiourea. The scope of this unprecedented transformation has been evaluated with electron-rich and electron-poor phenylthioureas.
O
O
O
H
N
S
N
Cl
Cl
K2CO3 (5 mol %)
PEG-400, 80 oC
X
Cl
S
X
H
N
Cl
O
N
H
NH2 K2CO3 (5 mol %)
PEG-400, 80 oC
H2O
O
+ X
NH2
S
Keywords: monosubstituted thiourea; chloroacetylchloride; PEG-400; thiazolidine-2,4-dione
1.
Introduction
The mechanism of thiazole-2-imine formation has not been well understood leading to the proposal of incorrect structures for the products obtained by the reaction of thiourea analogs with αhaloketones by two independent research groups (1). Based on the principle of hard–soft reactivity,
i.e. hard nucleophile attacks on hard electrophile and the soft nucleophile on soft electrophile, we have suggested an alternative reaction mechanism for the formation of thiazole-2-imine. Our mechanism is supported by isolating the reaction intermediate, confirming its structure and that of the products by X-ray crystallography (2). Having understood the reactivity of thioureas toward α-haloketones, recently, we have suggested an alternative structure for the product obtained by the reaction of thiourea with chloroacetylchloride (3). The structure of the product is found to
have the 2-imino-4-thiazolidinones moiety (3) and not the thiohydantoin as has been reported previously by another group (4).