Facile Metal-Free Synthesis of 3-Aryl-4-Substituted Coumarins fromO-Hydroxy Carbonyl Compounds

Microwave-Assisted Efficient Synthesis of 2-Hydroxydeoxybenzoins from the Alkali Degradation of Readily Prepared 3-Aryl-4-hydroxycoumarins in Water

“…This method avoids the use of poisonous pyridine. 10,37) More importantly, the hydrolysis of methyl 2-(2-arylacetoxy) benzoates 1 was rarely observed (except in the synthesis of compound 2j, vide infra), which readily takes place under the reported conditions, such as K 2 CO 3 -refluxing acetone, 35,36) solvent-free Na at 200°C 38) and lithium bis(trimethylsilyl)amide (LiHMDS) (or NaHMDS)-THF at −20°C. 39) This condition was applicable for a wide range of methyl 2-(2-arylacetoxy) benzoates 1 bearing both electron-donating and electron-withdrawing substituents ( Table 2).…”

“…In addition, it is reported that 4-hydroxy-3-phenylcoumarins can be prepared from the phase transfer catalyst-mediated one-pot reaction of methyl 2-hydroxybenzoates with arylacetyl chlorides. 35,36) Therefore, we also carried out the reaction in the presence of ammonium salts (entries 10-13). Thus, compound 2a was prepared in 47-75% yields in the presence of K 2 CO 3 -BnEt 3 NCl.…”

“…Because methyl 2-(2-arylacetoxy) benzoates 1 are readily hydrolyzed under reported conditions [35][36][37][38][39] and 3-aryl-4-hydroxycoumarins 2 are key intermediates for the synthesis of 2-OH-DBOs 3, we firstly revisited the intramolecular Claisen condensation reaction of methyl 2-(2-phenylacetoxy)benzoate 1a in acetone as a model reaction to search for the optimized reaction conditions. The results are summarized in Table 1.…”

Copper-catalyzed oxidative esterification of ortho-formyl phenols without affecting labile formyl group

“…No significant increase in the yield of 3 was observed when extending or shorting reaction time (entries 11 and 12). Other solvents, such as PhCl, toluene, and DCE, were proved to be less efficient than H 2 O (entries [13][14][15]. Higher or lower temperatures seemed to be inappropriate for the reaction (entries 16 and 17).…”

Green synthesis of 3-(1-naphthyl), 4-methyl-3-(1-naphthyl) coumarins and 3-phenylcoumarins using dual-frequency ultrasonication

“…Microwave irradiation has also been used for the synthesis of 3-phenyl and 3-naphthylcoumarins using DMSO as solvent [21]. Another method involves esterification of 2-hydroxybenzaldehydes in the presence of POCl 3pyridine followed by cyclisation of 2-arylacetoxysalicylaldehyde with KOH in pyridine [22]. The methods above have disadvantages like the use of hazardous solvents, longer reaction time, lower yields, etc.…”