A novel synthesis of precocenes. Efficient synthesis and regioselective O‐alkylation of dihydroxy‐2,2‐dimethyl‐4‐chromanones

The reactions of trihydroxybenzenes 1a‐c and 3‐methylbut‐2‐enoic acid ( 2 ) in a zinc chloride/water/phosphoryl chloride system afford either the new trihydroxyphenylbutenone derivatives 3b,c or dihydroxy‐2,2‐dimethyl‐4‐chromanones 4a‐c in good yields. Compounds 3b,c can be cyclized in high yields to 4b,c in 5% sodium hydroxide solution. Regioselective O ‐alkylation of 4a‐c leads to 5a‐f in good yields. O ‐Alkylation of 5a‐f , followed by reduction and dehydration, results in the formation of precocene 3 ( 7d ) and its regioisomer 7a‐c,e,f . Methylation of 4a‐c gives 6g‐i . Subsequent reduction and dehydration affords precocene 2 ( 7h ) and its regioisomers 7g,i .