Synthesis of Indoles: Tetrahydropyrazino[1,2-a]indole-1,4-dione and Pyrazino[1,2-a]indole-6,13-diones from Piperazine-2,5-diones
The readily available piperazine-2,5-dione has been used to prepare both 1:1 (1–3), with stereotopic methylene protons; and 2:1 (4–6) arylmethylenepiperazine-2,5-diones in above average yields. The halo-derivatives, 1, 4 and 5 were cyclized to pyrazino[1,2-a]indoles, 7–9, using copper bronze. Indole compounds 7 and 9 were further treated, separately, with lithium aluminium hydride, sodium borohydride, lithium hydroxide monohydrate and butyl lithium to yield 2-substituted indoles 10–13.
Keywords: Indoles, piperazine-2,5-diones, arylaldehydes, 1:1 adducts, 2:1 adducts.
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