Preparation of 3,5-Disubstituted Pyrazoles and Isoxazoles from Terminal Alkynes, Aldehydes, Hydrazines, and Hydroxylamine

The
reaction of terminal alkynes with n-BuLi,
and then with aldehydes, followed by the treatment with molecular
iodine, and subsequently hydrazines or hydroxylamine provided the
corresponding 3,5-disubstituted pyrazoles or isoxazoles in good yields
with high regioselectivity, through the formations of propargyl secondary
alkoxides and α-alkynyl ketones. The present reactions are one-pot
preparation of 3,5-disubstituted pyrazoles from terminal alkynes,
aldehydes, molecular iodine, and hydrazines, and 3,5-disubstituted
isoxazoles from terminal alkynes, aldehydes, molecular iodine, and
hydroxylamine.