ISSN:
1434-193X
Keywords:
Quinodimethanes
;
Cycloadditions
;
Thiazole derivatives
;
Quinones
;
Regioselectivity
;
Chemistry
;
General Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Treatment of 4,5-bis(dibromomethyl)thiazole (1a) with sodium iodide in DMF led to 4,5-bis(bromomethylene)-4,5-dihydrothiazole (2a). Trapping the latter in situ with dienophiles afforded directly the aromatized cycloadducts. Starting with 5-hydroxynaphthoquinone or its 2- and 3-bromo derivatives 6 gave a mixture of the tetracyclic quinones 10 + 11 from which the 1,6-regioisomer 10 predominates. Using acrylate dienophiles gave 6-substituted benzothiazoles 13 as the major products. The regiochemistry of the cycloadditions between 2a and naphthoquinones 6 agrees with the predictions of the frontier molecular orbital theory. In contrast, the regioselectivity observed from 2a and acrylate dienophiles 12, similar to that previously obtained with 5-bromomethylene-4-methylene-4,5-dihydrothiazole (2b), is opposite to that predicted and could be better accomodated by a competitive Michael addition followed by a cyclization-elimination step.
Type of Medium:
Electronic Resource
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