During the last decade we had investigated the acid-catalyzed reaction of hydroquinone derivatives with cycloalkendiols, cycloalkadiens and cycloalkandiols. The reaction of trimethylhydroquinone (1) with cycloalkendiol (8) afforded isomeric benzofuranols 11 and 12. Their formations were interpreted as the result of competing [1,3]- and [3,3] (Claisen) rearrangements of the initially formed allyl aryl ether (9), followed by acid-catalyzed cyclization. As an extension of this research we have examined the acid-catalyzed reaction of dialkoxyhydroquinone (18) with diol 8. The reaction proceeded by similar mechanism as discussed above, but the products of the rearrangement steps (e.q. 22) underwent an oxido-reduction process with the starting compound (18). The result was the facile formation of monoalkoxybenzofurans (21 and 24). The reaction of hydroquinone 1 with cycloalkane-1,3-diol (26) led to the formation of two compounds. Besides the expected benzofuran (29) spiro compound 33 was formed as major product. Here the [l,3]-rearrangement was followed by ring contraction and [1,2]-H shift (30→33). The reaction between dialkoxyhydroquinone (18) with cycloalkane-1,2-diol (34) afforded benzo[1,4]dioxine derivative (37). Besides this new one-pot synthesis of dioxine, we could prepare the cycloalkanobenzofuran (39) and spiro compound (38) by continuous separation of water formed in the initial step of the reaction. We have extended our investigation for the reaction of naphthols (40,41). From these reactions naphthofurans (45,48) were isolated in good yields.
|Number of pages||5|
|Journal||Magyar Kemiai Folyoirat, Kemiai Kozlemenyek|
|Publication status||Published - márc. 2004|
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