|Benzo-1,3-dioxoles and LTA||Bookmark|
This post is more a reaction/addition to Post 405635 (demorol: "Cheap aromatic iodination & bromination", Novel Discourse) In that thread, I mentioned I read something about the formation of quinones when e.g. benzene-1,3-dioxole would be reacted with LTA (lead tetraacetate). I found some of my old notes on the subject, since I had a dream once reacting LTA with benzene-1,3-dioxole to obtain new precursors. Allow me...
Taken from: Comprehensive Heterocyclic Chemistry, Vol 6: Five membered rings with two or more O, S or N atoms Chapter: Dioxoles and oxathioles
p 766: fused benzene rings
In electrophilic substitution reactions of benzo-1,3-dioxoles, only para-derivatives with respect to the oxygen atoms are formed. This differs from benzo-1,4-benzodioxanes where some ortho-isomer is obtained as well, and probably reflects the coplanarity of the rings in benzodioxoles resulting in an increased mesomeric effect <81H(15)1395>. Benzo-1,3-oxathiole derivatives undergo electrophilic substitution at the 5-position, i.e. para to the oxygen atom <53JCS1514>, although attack at the sulfer atom may be a complicating factor. 2,2-disubstituted benzo-1,3-dioxoles are oxidized by lead tetraacetate (LTA) to 5-acetoxy and 5,6-dione derivatives, as shown in equation (11) <80AJC527>. If the 2-position is not blocked, oxidation occurs there preferentially. The quinones are probably formed via a tetraacetoxy intermediate in a manner analogous to the oxidation of naphtyl ethers <79AJC1749>. As expected, metallation with n-BuLi takes place ortho to the oxygen atom in both systems provided that the 2-position is blocked.
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