General Papers ARKIVOC 2007 (i) 180-188
1
CO2R RN
CO2R S
R1N
S R2N
2
RN
OO
(1) (2) We have considered the reaction of thiosemicarbazone derivatives with dimethyl acetylene dicarboxylate and diethyl acetylene dicarboxylate to synthesis thiazolines, and to find the influence of the nature of electron donor group on the progress of this reaction, in addition on the structure of the resulting products. It should be noted that the reaction of thiosemicarbazone derivatives which contain two N-H, NH2 and one S-group with DMAD and DEAD have not been described in the literature thus far.
Results and Discussion
In continuing our interest in the synthesis of heterocyclic compounds such as 1,3-thiazinones7 and other heterocyclic compounds. We would like now to report the synthesis of thiazoline compounds from thiosemicarbazone derivatives possessing two N-H, NH2 groups and one S=C bond which react with DMAD and DEAD to give thiazoline. In this reaction the sulfur atom attacked the triple bonds and a thiolactam is formed, followed by the aminolyses of an ester group8. This reaction can lead to the structures type (1), and type (2). Both products have been claimed, although structure type 2 has not been confirmed. In this investigation we report three methods for the synthesis of thiazolines: a) thiosemicarbazone is dissolved in ethyl acetate then DMAD or DEAD is added to this solution, reaction was carried out with a stirring for 2.5-5 hr at ambient temperature, b) a facile synthesis via a one-pot three-component reaction between thiosemicarbazide, aldehyde/ketone and DMAD or DEAD in the present of catalytic amounts of acetic acid, thiosemicarbazide and aldehydes are converted in-situ to thiosemicarbazone, next the thiosemicarbazone are reacted with DMAD or DEAD under microwave irradiation and solventfree condition to produce thiazolin in 95-98% yields, c) in the third method, thiosemicarbazone was mixed with DMAD or DEAD, then the reaction was subject to microwave irradiation under free solvent conditions at short experimental time. The following results were obtained, formation of 1c, after 3 h in method a, 3 min in method b and 5 min in method c. A plausible mechanism is shown below, scheme (1). Compound 1c reveals NH group at 3180 , C-H absorption of thiophene ring at 2780-3081 cm-1 ,carbonyl groups at 1741, 1661 cm-1 and C=N, C=C at 1666, 1641, 1617 cm-1 in the IR spectrum. The 1H NMR spectrum of 1c indicated one singlet quite down field at (d 12.60 ppm) which is the proton of NH amide, thiophene ring protons at 7.75, 7.57, 7.18, vinyl proton at 6.64 and methoxy protons at 3.76 ppm. The 13C NMR spectrum of 1c indicated carbonyl group carbons at 165.69, 165.48, 159.16 (C=N), 152.77 (S-
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