Yan He, Xinying Zhang, Liangyan Cui
Apr 1, 2013
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Influential Citations
12
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Journal
Chemistry, an Asian journal
Abstract
Functionalized benzenes, in particular, carbonylor iodosubstituted benzenes, are attractive synthetic targets as they are not only commmon structural units in natural products and pharmaceuticals, but also among the most commonly used precursors in organic synthesis. While direct functionalization of aromatic starting materials is often used to prepare the required functionalized benzenes, construction of aromatic rings from the easily obtainable acyclic units constitutes another efficient way for this purpose. Cycloaromatization of enyne–allenes through a radical intermediate, known as the Myers–Saito cyclization, is documented as an efficient method for the preparation of benzenoid compounds. However, the utility of this strategy is compromised as the enyne–allene precursors are usually obtained through multi-step processes that employ expensive catalysts and reagents, or generated in situ through noble transition-metal-catalyzed sigmatropic rearrangement of propargylic acetates or propargyl vinyl ethers. In our recent study on the chemistry of allene derivatives, we have developed a synthetic approach toward 2Hpyran-2-ones through the tandem reaction of 3-hydroxyhexa-4,5-allenic esters. The reaction is thought to be initiated by an acid-promoted dehydration of the tertiary alcohol followed by hydration of the allene moiety and an intramolecular esterification of the in situ formed enol unit. In light of the high efficiency and mild conditions involved in the above-mentioned process, we hypothesized that an acidic promoter might trigger the Myers–Saito process through dehydration of hepta-1,2-dien-6-yn-4-ol to give the required hepta-1,2,4-trien-6-yne. Subsequent cycloaromatization of the enyne–allene intermediate would afford a biradical intermediate, from which a meta-substituted toluene molecule is supposed to be formed (Scheme 1). To check the feasibility of the above proposal, 4-phenylhepta-1,2-dien-6-yn-4-ol (2 a) was prepared from 1-phenylbuta-2,3-dien-1-one (1 a) and propargyl bromide under the promotion of zinc and was then treated with H2SO4 in CH2Cl2 (Scheme 2) under reflux. To our disappointment, the