1H-indazoles as synthetic auxiliares for the synthesis of secondary aromatic amines

Methodol. of alkylation of arom. amines using 1H-indazoles as synthetic auxiliaries is reported. Thus, indazoles (I; R,R1 given: H,H;Me,H;CO2Me,H;H,Me) were prepd. and reacted with several aniline derivs, and o-aminopyridine to give the corresponding aminals (II;R,R1 as above; R2= H,Me,MeO; X=CH,N) in good yields. II were smoothly converted to into the corresponding N-alkylamines by redn. with LiAlH4 in ether at room temp. in only 5 min. N-alkylation at the amino group of 2-aminopyridine is very difficult to achieve due to preferential reaction at the pyridine nitrogen atom to give a quat salt. The alkylation of 2-aminopyridine occurred only at the amino group; thus, NaBH4 redn. of II(R=CO2Me,R1=R2=H,X=N) and LiAlH4 redn. of II(R=R1=R2=H,X=N) afford 2-(methylamino)pyridine in good yield.