Divergent synthesis of withasomnines via synthesis of 4-hydroxy-1H-pyrazoles and Claisen rearrangement of their 4-O-allylethers

4-Hydroxypyrazoles were synthesized by the alkaline hydrolysis of the Baeyer–Villiger oxidation products of 4-formylpyrazoles. This new synthesis of 4-hydroxypyrazoles was applied to the divergent synthesis of withasomnine alkaloids in a unique strategy, for which the key steps included the regioselective Claisen rearrangement of their 4-O-allyl-4-hydroxy-1H-pyrazoles and a Suzuki coupling of 4-trifluoromethanesulfonyloxy-1H-pyrazoles and arylboronic acids.