p-Toluenesulfonic acid → 8,8,10-trimethyl-2H,8H-benzo[1,2-b;5,4-b']dipyran-2-one

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A solution prepared from 5.0 mmol of 8-methyl-7-hydroxycoumarin and 6.0 mmol of 2-methyl-3-butyn-2-ol in 40 ml of xylene containing 0.095 g (0.50 mmol) of p-toluenesulfonic acid was refluxed with magnetic stirring for 4 hours. The solvent was distilled off in vacuo and the oily contents of the flask chilled in an ice-salt water bath to induce crystallization. The white microneedles, 33% yield, were recrystallized from methanol to analytical purity, m.p. 105°-107° C. (lit. m.p. 106°-107° C.). The 1H-NMR spectrum was also identical to that reported, see P. Rodighiero et al., reference cited above.

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