REGIOSELECTIVE AND STEREOSELECTIVE 1,3-DIPOLAR CYCLOADDITION REACTIONS OF ETHYL DIAZOACETATE TO 3-SUBSTITUTED 2H-1-BENZOPYRAN-2-ONES

The cycloaddition of ethyl diazoacetate to 3-substituted 2H-1-benzopyr an-2-ones, 1, gave the benzopyrano[3,4][2]pyrazolines 11, the benzopyr ano[3,4]cyclopropanes 12, the benzopyrano[3,4-c]pyrazole 13 and the (o -hydroxy)phenyl-pyrazoles 14 as the main products. When the cycloaddit ion was performed in the presence of silica gel the rate of the reacti on increased substantially and the yields of the cyclopropane derivati ves 12 were more than doubled Ethyl diazoacetate adds to benzopyran-3, 4-double bond regio- and stereo-selectively giving the endo-form of th e initial cycloadduct 15, which being unstable, is then transformed ma inly to the above mentioned compounds.