A Synthetic Route to Hexahydro[1,4]oxazino[2,3-h] and [3,2-j]β-Carboline Derivatives

Abstract

Convenient methods for the regioselective formylation of tetrahydro[1,4]oxazino[2,3-f] and [3,2-g]indole derivatives 3 and 4 are described. The obtained formyl derivatives 6 and 8 were further transformed in four steps into the unknown hexahydro[1,4]oxazino[2,3-h] 1 and [3,2-j]β-carbolines 2.

Key words

oxazinoindoles - regioselective formylation - Vilsmeier-Haack reaction - Rieche reaction

References

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13

Compound 6a (n = 1, R = H) could be also transformed into the corresponding nitroethyl derivative of type 10 in a total yield of 69%. Hydrogenation over Raney nickel afforded the ethylamine derivative as a relatively stable solid (mp 103-105 °C; 84% yield), which upon heating in toluene afforded the corresponding lactam of the type 11 in only 34% yield. (DBU gave only degradation products).