In this paper, a basic method to access new multicomponent reactions (MCRs) is reported. The mechanism of these MCRs is based on the trapping of methyleneintermediates, formed in situ by reaction of formaldehyde with electron-rich carbons, with alkene, thiol or indole derivatives. According to our strategy, a wide range of valuable skeletons has been obtained in a one-pot reaction, thus allowing a
The Chemistry of Coumarin Derivatives. Part VI. Diels-Alder Trapping of 3-Methylene-2,4-chromandione. A New Entry to Substituted Pyrano[3,2-c]coumarins
3-Methylene-2,4-chromandione (1) can be generated from dicumarol or from paraformaldehyde and 4-hydroxycoumarin. 1 is a versatile substrate for cycloaddition reactions. Depending on the reaction partner, 1 can behave as an ambident heterodiene or as a dienophile. The reaction was investigated with a series of olefins and dienes, including several isoprenoids. Some generalizations could be drawn and rationalized in terms of HOMO-LUMO interactions. The reaction of 1 and certain asymmetrically substituted olefins gives pyrano[3,2-c]coumarins in a highly regio- and chemoselective way. As an application of this reaction to natural products chemistry, a concise (three steps) synthesis of the prenylated coumarin (+/-)-isoferprenin (35a) is reported.
Acid-Catalyzed Regiodivergent Annulation of 4-Hydroxycoumarins with Isoprene: Entry to Pyranocoumarins and Pyranochromones
An acid‐catalyzed regiodivergentannulation of biomass‐derived 4‐hydroxycoumarins with isoprene is developed, providing a facile access to pyranocoumarins and pyranochromones.