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The chemistry of coumarin derivatives synthesis of 3 alkyl 4 hydroxycoumarins by reductive fragmentation of 3 3' alkylidene 4 4' dihydroxybiscoumarins


The chemistry of coumarin derivatives synthesis of 3 alkyl 4 hydroxycoumarins by reductive fragmentation of 3 3' alkylidene 4 4' dihydroxybiscoumarins



Helvetica Chimica Acta 74(7): 1451-1458



ISSN/ISBN: 0018-019X

DOI: 10.1002/hlca.19910740708

Treatment of 3,3'-alkylidene-4,4'-dihydroxybis[coumarins] 1 with NaBH3CN in refluxing MeOH affords 3-alkyl-4-hydroxycoumarins 2 and 4-hydroxycoumarin (3; Scheme 1). The reaction might take place via hydride trapping of alkylidenechromandiones C formed from 1 in a retro-Michael reaction. Such a retro-Michael reaction of 1 might be biologically relevant. The presence of C during the reductive fragmentation 1 .fwdarw. 2 is suggested by Diels-Alder and nucleophilic trapping of the alkylidenechromandiones C as well as from cross-over experiments with coumarins other than 3 (see Scheme 2). The reductive fragmentation of 1 allows the chemo- and regioselective synthesis of a variety of 3-alkyl-4-hydroxycoumarins 2 (see Table).

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