CCLII.—Hydroxy-carbonyl compounds. Part IV. The preparation of coumarins and 1 : 4-benzopyrones from pyrogallol

General Methods of Preparing Chromones

“…4,6-Dimethoxy-3-ethyl-2-hydroxyacetophenone was unaffected by heating at 170-1 80" for 8 hr with acetic anhydride and sodium acetate. 206 acylated29 ,l35,137,140,152,l53,159,162,16~ ,177,184,185,190-l98 but not always; 167,182,196,[199][200][201][202] Replacing the methyl of the ketone group by higher alkyl or alkoxyl may alter the chromone/coumarin ratio in the product but does not otherwise affect the reaction; there are examples of 3-alky1-,68,141-L52, '76,204,207-209 3-aralkyl-,87, prepared in this way. On the other hand, 2'-hydroxyphenacyl bromide (87, 135,137,151.159,160,210 3-a]koxy-, '36,13n.195 and N-arylcarbamoylchromones88 520 General Methods of Preparing Chromones R = H , X = B r ) was converted in 60% yield into the 3-acetyloxychromone (88),143,211 and 5'-chloromethyl-2'-hydroxypropiophenone gave a good yield of 6-acetoxymethyl-2,3-dimethylchromone,212 but the chlorine atom in 2'-hydroxy-5'-methylphenacyl chloride (87, R = Me, X = C1) was resistant to acetolysis and yielded 3-chloro-2,6-dimethylchromone (89) together with a smaller amount of 3-hydroxy-2,6-dimethylchromone.143 6-Acetyloxy-3-chloro-2-methylchromone has been similarly prepared,213 but 2',4'-diacetyloxyphenacyl chloride under the Kostanecki-Robinson reaction conditions gave only the tria~etate.~'~ aoH + Ac20 + AcONa R COCH2X…”

“…The yield of 3-methyl-4-thiochromone (199) is not stated, and some 323-1,2-dithiole-3-thione (200) is also formed.349 + P,S, -COCHMeCHO 5 ( 198) 190. 191.…”

Neoflavones. 2. Methods for Synthesizing and Modifying 4-Arylcoumarins

“…Condensing agents in this reaction include sulfuric [1, 2, 4, 7, 9, 11, 16, 18, 20-22, 24, 26-28, 30, 32, 33, 35, 36, 40, 44, 49, 52-55, 59, 60, 61, 63, 66-73], phosphoric [5,45], and trifluoroacetic acids [10], phosphoryl chloride in benzene [25], phosphorus pentoxide [34,36,37], boron trifluoride etherate [15,29,43], zinc chloride [1, 2,33], a solution of HCl in absolute ethanol [3, 6, 8, 11-13, 31, 38, 39, 41, 45, 47-50, 57, 58, 61, 62, 65, 69], and HF [19].…”

“…Phenols that have been used in the Pechmann condensation include resorcinol [1-15], 3-methylphenol [16,17], 4-methylphenol [18,19], 2,4-dimethylphenol [20], 3-methoxyphenol [7,21], 2-methylresorcinol [10,[22][23][24], orcine [10,14,25], 4-chlororesorcinol [10,26], 2-bromoresorcinol [27], 4-ethylresorcinol [28,29], β-resorcinolic acid methyl ester [30], 5-pentadecylresorcinol [31], 4-ethyl-2-acetylresorcinol [28], 2-methylhydroquinone [32], 2-ethylhydroquinone [32], pyrogallol [5,10,11,15,33,34,59,64], 4-ethylpyrogallol [35], pyrogallol-4-carboxylic acid ethyl ester [35], phloroglucinol [10,11,13 15,33,[36][37][38][39][40][41][42][43]…”

“…The structures of the products from condensation of o-hydroxyarylketones and anhydrides of the corresponding acids in the presence of base depend on many factors. The starting materials for synthesizing substituted 4-arylcoumarins 1 are o-hydroxybenzophenones of various structure and acetic anhydride in the presence of potassium or sodium acetates [34,37,58,[75][76][77][78][79][80][81][82][83][84][85][86][87][88][89][90][91][92][93][94].…”