Umbelliferone alkylated

Many other natural coumarins have a more complex carbon framework and incorporate extra carbons derived from an isoprene unit (Figure 4.33). The aromatic ring in umbelliferone is activated at positions ortho to the hydroxyl group and can thus be alkylated by a suitable alkylating agent, in this case dimethylallyl diphosphate. The newly introduced dimethylallyl... 

Alkylation of umbelliferone with chloromethyl esters of various ahphatic acids affords the corresponding acyloxymethyl ethers (e.g. 27) in good yields [38]. These substrates undergo lipase/esterase-catalyzed hydrolysis in buffer to form umbelliferone (Scheme 1.9) [39]. The mechanism probably involves an unstable hemi-acetal intermediate, which spontaneously reacts to formaldehyde andumbeUiferone... 

The substrates can also be prepared in a two-step sequence involving alkylation of umbelliferone with 2-chloroketones followed by Baeyer-Villiger oxidation. The sequence is particularly interesting for obtaining the fluorogenic lactones 28 and 29, which only react with esterases [40]. 

Biosynthesis of Phenylpropanoids and Related Compounds 203 4.3.1.2 Alkylated umbelliferone... 

Umbelliferone is the pivotal metabolite in the pathways to substituted coumarins and furano- or pyranocoumarins. Its 7-0-methylation to herniarin (Fig. 4.3) or 0-prenylation and C-alkylation reactions are often observed in coumarin-producing higher plants where the prenylation at C-6 or C-8 mark the entry to the routes branching linear from angular furano- and pyranocoumarins (Fig. 4.5). In Ruta graveolens and Ammi rmjus, the prenylation reactions are catalysed by particulate enzymes (Hamerski et at, 1990), and... 

By reaction of phenols with bifunclional molecules, which are able to alkylate and to esterify, several coumarin derivatives have been prepared using H-Bela as the catalyst. Thus resorcinol and propynoic acid react at 150 °C in p-chlorotolucnc as the solvent towards the perfumery ingredient umbelliferone (7-hydroxycoumarin) in good yield, 60 %, [84], Amberlyst-15 gave 40 % yield. II-Beta catalyzes the esterification as well as the ring closure alkylation step. 

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