Design and synthesis of a new indazole library: direct conversion of N-methoxy-N-methylamides (Weinreb amides) to 3-keto and 3-formylindazoles

Nucleophilic addition of Grignard or lithiated reagents on the new Weinreb amides 3 and 4 afforded efficiently the corresponding ketones and allowed the design and synthesis of a new indazole library. These 3-ketoindazoles were obtained by a direct and original conversion of N-methoxy-N-methylamides with good yields. Furthermore, the reduction of 3 with LiAlH4 furnished the corresponding aldehydes as a versatile and efficient pathway to 3-formylindazoles.