5-CHLOROPYRAZOLE-4-CARBALDEHYDES AS SYNTHONS FOR INTRAMOLECULAR 1,3-DIPOLAR CLYCLOADDITIONS

A general method is described to transform the readily available title compounds into tri- and tetracyclic heterocycles, first by substituti ng the chlorine atom by an unsaturated thiolate or alkoxide, and then by modifying the aldehyde function into a 1,3-dipole. As 1.3-dipoles, nitrile oxide, nitrone, nitrile imine, azomethine ylide and azomethine imine groups were generated from the 5-allylsulfanyl-4-formylpyrazole 7, which resulted in intramolecular cycloaddition and formation of th e heterocycles shown in Scheme 2. The other pyrazoles 22, 23, 26, 30 a nd 33 were converted via intramolecular nitrile oxide cycloaddition (I NOC) into fused dihydroisoxazoles. A limitation to the method is the C laisen rearrangement which occurs when the allyl ether 26 or the prop- 2-ynyl ether 30 is used.