Alkylation of pyrazolones via the Mitsunobu reaction
Results and discussion
Several reactions of pyrazolones 1 and 4 in various solvents (tetrahydrofuran, dichloromethane, chloroform, acetonitrile, benzene) using methanol as the alkylating agent were performed.
Additionally, educt 4a was also treated with benzyl alcohol, isopropyl alcohol and 2,3-epoxypropanol. The
results of our reaction runs are given in Table 1. In many cases mixtures of
both isomers were obtained with the O-alkylated species predominating. However, using benzene or THF as the solvent
often led to selective O-alkylation (for instance 4a and methanol, isopropyl alcohol, benzyl alcohol and 2,3-
epoxypropanol, respectively). In conclusion, this mild and versatile approach seems to be a useful access to
N- and O-alkylation products of pyrazolones, particularly to special 5-alkoxypyrazoles being not
(or not easily) amenable from reaction of pyrazolones with conventional alkylating agents.