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Synthesis 2007(6): 819-823  
DOI: 10.1055/s-2007-965929
SHORTPAPER
© Georg Thieme Verlag Stuttgart · New York

Synthesis of 2-Arylbenzothiazoles by DDQ-Promoted Cyclization of Thioformanilides; A Solution-Phase Strategy for Library Synthesis

D. Subhas Bose*, Mohd. Idrees, Bingi Srikanth
Organic Chemistry Division III, Fine Chemicals Laboratory, Indian Institute of Chemical Technology, Hyderabad, 500 007, India
Fax: +91(40)27160387; e-Mail: dsb@iict.res.in; e-Mail: bose_iict@yahoo.co.in;
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Publication History

Received 10 December 2006
Publication Date:
08 February 2007 (online)

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Abstract

Several substituted benzothiazoles were synthesized by the intramolecular cyclization of thioformanilides using 2,6-dichloro-3,5-dicyano-1,4-benzoquinone (DDQ) in dichloromethane at ambient temperature in high yields. The resulting 2-arylbenzothi­azoles were separated from the reduced DDQ byproduct 4,5-dichloro-3,6-dihydroxyphthalonitrile by treatment of the reaction mixture with a strongly basic ion-exchange resin. This protocol offers a high degree of flexibility with regard to the functional groups that can be placed on the benzothiazole ring or 2-aryl moiety, which in turn generates scaffolds for parallel synthesis.

Key words

thioformanilide - solution phase - cyclization - 2,6-dichloro-3,5-dicyano-1,4-benzoquinone - benzothiazole - sulfanyl radical

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The material loss, as indicated by crude yields in Table [1] , was mainly due to the binding of the product to the resin. In order to keep the same method as used in the final library synthesis, we did not use excessive solvent, which was limited by the volume of the collection plate, to wash the resin to improve the yields