Abstract
It is shown that 4- or 8-[(E)-styryl]-substituted azulenes can easily be prepared from 4- or 8-methylazulenes in the presence of potassium tert-butoxide (t-BuOK) with the corresponding benzaldehydes in tetrahydrofuran (THF) at −5 to 25° (see Schemes 1 and 2). 6-(tert-Butyl)-4,8-dimethylazulene (5) with both Me groups in reactive positions leads to the formation of a mixture of the mono- and distyryl-substituted azulenes 6 and 7, respectively (Scheme 3). Vilsmeier formylation of 6 results in the formation of 3 : 2 mixture of the azulene-carbaldehydes 8a and 8b, which can be separated by chromatography on silica gel. Reduction of 8a and 8b with NaBH4 in trifluoroacetic acid (TFA)/CH2Cl2 gives the 1-methyl forms 9a and 9b, respectively, in good yields (Scheme 4). The latter two azulenes are not separable on silica gel.
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