Rhodium(II)-catalyzed reactions of 3-diazo-2,4-chromenediones. First one-step synthesis of pterophyllin 2

Rhodium(II)-catalyzed reactions of 3-diazo-2,4-chromenediones 1-3 with a va riety of substrates are described. Reactions of 1 with nitriles, isocyanate s, and ketones give the corresponding 5-membered heterocycles in moderate y ields, whereas those of 1 with acid chlorides afford alpha-chloroenones in moderate yields. Reactions of 1 with electron-rich and -deficient olefins s uch as vinyl ethers and allyl iodide give dihydrofurocoumarins as a single compound, whereas those of 3 with vinyl esters afford either angular dihydr ofurocoumarin and a linear product or a rearranged product as an isomer. Fu rthermore, this novel method has been applied to the synthesis of the natur al pterophyllin 2 isolated from Ekebergia pterophylla. (C) 1999 Elsevier Sc ience Ltd. All rights reserved.