Synthetic methodology study demonstrates amine-catalyzed cascade annulation between beta-acetoxy allenoates and bisnucleophiles, indicating an efficient pathway to substituted thiophenes and pyrroles.
The amine-catalyzed cascade (3 + 2) annulation and aromatization sequence between β'-acetoxy allenoates and 1,2-bisnucleophiles has been developed. When 1,4-dithane-2,5-diol is used as the bisnucleophile partner, the corresponding reaction affords fully substituted thiophene-2-carbaldehyde, which might proceed via the amine-catalyzed (3 + 2) annulation and subsequent oxidative aromatization. The reaction protocol is also applicable to a 2-tosylamino-carbonyl bisnucleophile, wherein the (3 + 2) annulation is followed by 1,2-elimination of a tosyl group and isomerization to give a 1H-pyrrole product.
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Ni et al. (2016) studied this question.