Reactions of 1,2,3-Trihydroxybenzenes

4-Phenyl-5,7-dihydroxy-3,4-dihydrocoumarin was formed in 87% yield from phtoroglucinol and Meldrum s acid in pyridine and addition after 10 mins, of benzaldehyde followed by stirring of the reaction mixture at 70-75°C for 1 hour 

By contrast, reaction of phloroglucinol with 3,3-dimethylacrylic acid (3-methylbut-2-enoic acid) in the presence of anhydrous aluminium chloride and phosphorus oxychloride by agitation during 5 hours at ambient temperature gave a 90% yield of 2,2-dimethyl-5,7-dihydroxychroman-4-one (ref.9). 

2-(4 -Acetoxy-3,5-dimethoxyphenyl)-5,7-diacetyl-3-acetoxyflav-3-ene has been synthesised from the quinonemethide shown by addition to a benzene/dimethyl formamide (25 1) solution of phloroglucinol followed by reaction for 2 mins, in the presence of a catalytic quantity of 4-toiuenesulphonic acid to give initially the open chain C-alkylated intermediate in 48% yield. This was stirred for 48 hours at ambient temperature in benzene/acetone containing silver oxide and was then acetylated with acetic anhydride/pyridine (ref. 10). 

Trimethylphloroglucinol (R = Me) and hexamethylenetetramine after refluxing in methanol during several hours afforded the aminoalkylated tetracyclic product indicated containing three 3,5-dimethylpiperid-4-one rings in 80% yield (ref.11). 

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