Facile One-Pot Synthesis of 3,5-Disubstituted 1H-Pyrazoles from Propargylic Alcohols via Propargyl Hydrazides
摘要:
A new and efficient metal-free, two-component, one-pot approach to a variety of 3,5-disubstituted 1H-pyrazoles has been developed from propargylic alcohols. This transformation proceeds via an acid-catalyzed propargylation of N,N-diprotected hydrazines followed by base-mediated 5-endo-dig cyclization leading to 3,5-disubstituted 1H-pyrazoles in good overall yields.
Pyrazoles direct: Propargyl alcohols undergo hydrazination when treated with p‐tosyl hydrazide in the presence of catalytic amounts of either Sc(OTf)3 or La(OTf)3 (see scheme; Tf=trifluoromethanesulfonyl). Propargylhydrazides are converted into either N‐tosyl or N‐H pyrazoles when treated with an acid or a base, respectively. The one‐step acid‐catalyzed hydrazination/cyclization of propargyl alcohols