A simple and efficient condition for Pechmann condensation for the synthesis of coumarins involving grinding of different phenols and b-ketoesters in the presence of p-toluenesulfonic acid at room temperature under solventfree conditions has been described. A faster reaction and higher yields compared to the conventional methods are the advantages of present protocol.
2-Hydroxybenzaldehydes 1a-e on reaction with malononitrile (2) in the presence of iodine as catalyst give 3-cyanocoumarins 3a-e in one step under thermal heating as well as under microwave irradiation. The latter conditions are much more efficient in terms of time (2-5 min) and yield as compared to the thermal conditions (2-2.5 h). Following a similar procedure, 3-cyano-4-methylcoumarins 3f-i were also prepared by the reaction of 2-hydroxyacetophenones 1f-i with 2.
BakerÁVenkataraman rearrangement of 2-aryloxyacetophenones and 2-cinnamoyloxyacetophenones to 2-hydroxydibenzoylmethanes and 2-hydroxybenzoylcinnamoylmethanes is the key step in the synthesis of flavones and 2-styrylchromones, a class of naturally occurring compounds and several other benzofuranone derivatives. A very simple and highly efficient eco-friendly procedure for BakerÁVenkataraman rearrangement has now been developed which involves the grinding of 2-aryloxyacetophenones/2-cinnamoyloxyacetophenones with pulverized potassium hydroxide in a mortar by a pestle and avoids the use of organic solvents at any stage of the reaction.
(2E,4E)‐1‐(2‐Hydroxyphenyl)‐5‐phenylpenta‐2,4‐dien‐1‐ones 1a, 1b, 1c, 1d, 1e on oxidative cyclization with mercuric acetate in dimethylsulphoxide have provided (Z)‐2‐((E)‐3‐phenylallylidene)benzofuran‐3(2H)‐ones 2a, 2b, 2c, 2d, 2e in good yields.
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