| 摘要 |
Dihydrofurochromones of the general formula IV in which R represents a lower alkyl group are made by the following series of reactions <FORM:0663418/IV (b)/1> The 6-hydroxy-5-acetylcoumaran II is prepared (1) by reacting 6-hydroxycoumaran with acetonitrile according to the Hoesch reaction, (2) by reacting 6-hydroxycoumaran with an acetylating agent, e.g. acetyl chloride, in the presence of a condensing agent such as aluminium chloride, or (3) by subjecting 6-acetoxycoumaran to the Fries reaction, i.e. by treatment with aluminium chloride in the presence of dry nitrobenzene. The 6-hydroxy-5-acetylcoumaran is then submitted to the Claisen reaction using an ester of the acid R-COOH to give the 6-hydroxy-5-b -ketoacylcoumaran III which is cyclo-dehydrated, e.g. by treatment with sulphuric or hydrochloric acid dissolved in alcohol or acetic acid, to yield the dihydrofurochromone IV. Examples are given in which R in the formul is methyl, ethyl or propyl. |
