2-Bromo-3-hydroxy-1,4-naphthoquinone

As thiazoles have significant aromatic character, they display poor reactivity in cycloaddition reactions. However, a theoretical study of the Diels-Alder reactions of a thiazole o-quinodimethane 83 with 2- and 3-bromo-5-hydroxy-naphthoquinones 84 and 85 has been carried out (Scheme 24) <2000T1701>. The findings from the PM3, molecular hardness, and ab initio (3-2 Gp) calculations of this study agree with the experimental results and support the statement that hydrogen bonding plays a crucial role on the regiocontrol of the cycloadditions. 

Bromo-3-hydroxy-l,4-naphthoquinone (bromolawsone) and 2,3-di-chloro-1,4-naphthoquinone react similarly [93CCC1191,93IJC(B)365]. Further examples have been reported (85MI1). 

A solution of 3.0 g 2-hydroxy-3-(y-phenyl)propyl-6-bromo-l,4-naphthoquinone in the required amount of benzene was stirred in 600 mL hot 1% NaOH solution, and the red solution was cooled to 0°C and treated with 189 mL 1% KMn04 also at 0°C. The solution becoming practically colorless (spot test) and then reaching a maximum intensity of red in 1 to 2 h. The yield of precipitated, nearly pure material was 36%. Crystallization from alcohol containing acetic acid afforded 3-hydroxy-2-(y3-phenyl)ethyl-6-bromo-1,4-naphthoquinone as golden yellow needles, m.p. 173-175°C. 

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