Unusual nicotinoylation of 4-phenyl-5,7-dihydroxycoumarin

In the present work, we report a convenient synthesis of 5- and 7-substituted-4-phenyl coumarins. In contrast to previous results obtained with 4-alkylcoumarins, nicotinoylation of 5,7-dihydroxy-4-phenylcoumarin with nicotinoyl benzotriazole or nicotinoyl azide selectively provides 5-O protected ester. The combination of the nicotinoylation reaction followed by tosylation-denicotinoylation yields 5-hydroxy-7-tosyloxy-coumarin derivative, which may be useful in the synthesis of inophyllum, a tetracyclic HIV reverse transcriptase inhibitor, as well as its analogues.