Chemoselective preparation of ketones by the grignard reaction of N-acylpyrazoles

N-Acylpyrazoles afford chemoselectively the corresponding ketones in good yields by the use of equimolar amounts of Grignard reagent. In the case of an optically active N-acylpyrazole, optical asymmetry was retained in comparable optical yield. Ketone formation by the Grignard reactions can be regarded as an important functionalization in a synthetic loop using pyrazoles as the auxiliary compound.