Synthesis of multi-functionalized benzofurans through the condensation of ninhydrin and phenols using SSA as a recyclable heterogeneous acid catalyst
A simple and efficient one-pot methodology has been developed for the synthesis of biologically important multi-functionalized 3-(2$$^{\prime }$$′-hydroxyaryl)-2-(2$$^{\prime }$$′-carboxyphenyl)benzofurans using silica sulfuric acid (SSA) as a heterogeneous acid catalyst in DMF medium. The significant advantages of this methodology are the use of SSA as a recyclable solid acid catalyst, operational simplicity, easy availability of the starting materials, and good yield of the products with high atom-economy.
Condensation of ninhydrin with phenols: Regioselective formation of diverse organic scaffolds and crystal structure studies
Abstract In the present work, a range of phenolic compounds have been reacted with ninhydrin in acid medium to afford different indanone-based molecules via regioselective C–C bond formation. Ninhydrin reacts with 2,7-Dihydroxynaphthalene and 4-cyanophenol in AcOH producing ortho selective adduct 3a and 3b respectively; however, unlike 3a remaining as cyclic hemiketal structure, 3b exists as ring-opened diketo form. On the other hand, ortho-substituted phenols like o-cresol, guaiacol, o-chloro/iodophenol condense with ninhydrin to accomplish para selective diarylated adducts 5a-d, whereas 3-methoxy phenol provides corresponding monoarylated adduct 5e as the major product. Different hydroxy benzoic acids deliver versatile scaffolds like diarylated indanone, indenofuran, benzofuran or spirolactone 7a-e depending upon the substitution pattern and acidity of the reaction medium. All the compounds are characterized by 1H and 13C NMR spectra. In the solid state, scissors-shaped molecule 5a has been found to form inclusion complex with disordered o-cresol molecule and function as building unit of supramolecular network. In the crystal structure of spirolactone 7d, anti-parallel motif of dipolar···dipolar (C O(δ−)···C(δ+) = O) interaction results ladder-like arrangement.
Phloroglucinol derivatives from Hypericum japonicum.
The isolation and identification of a new phloroglucinol derivative (2), a diterpenol (4), together with the known compounds flavesone (1) and sarothralen B (3), from the aerial parts of Hypericum japonicum are reported. Their structures were established by extensive spectral analysis and the structure of (3) has also been confirmed by a single crystal X-ray determination.