Synthesis of 3,4-dihydropyrazino[1,2-b]indazolesa
aReagents and conditions: (i) CDI, substituted ethylenediamine, pyridine, DCM, 5 h; (ii) 2-nitrobenzenesulfonyl chloride, lutidine, DCM, overnight; (iii) bromoketone/bromoacetate, DIEA, DMF, overnight; (iv) DBU, DMF, 30 min; (v) methanesulfonyl chloride, TEA, DCM, overnight; (vi) 50% TFA in DCM, 1 h; (vii) AcOH, 2 h; (viii) TEA, MeOH, overnight