compounds 4-20 easily underwent displacement reactions with a variety of piperazines to afford 2- ( 4-substituted or unsubstituted 1-piperazinyl ) derivatives 21-56 , of which 21 , 22 , 27 and 51 with unsubstituted piperazinyl group at position 2 are converted subsequently into 57-73 by alkylation , acylation , sulfonylation , or addition of isocyanates to the piperazine nitrogen .
C0031958
piperazines
C0031957
nitrogen