N-[2-(4,5-Dihydro-7-methoxy-1H-benzo[g]indol-1-yl)ethyl]acetamide (14.5 g) was treated with 50 ml of phosphorus oxychloride under argon and the mixture was stirred at 50° C. for 30 minutes. The cooled mixture was added to 5000 g of ice-water and treated with 500 ml of 28% sodium hydroxide solution. The mixture was extracted once with 1000 ml of methylene chloride and twice with 500 ml of methylene chloride each time, the organic phases were combined, dried with MgSO4 and freed from solvent. The residue, 14.6 g of brown oil, was chromatographed on 220 g of aluminium oxide (neutral, III) with methylene chloride as the eluent. 1.3 g of a total of 10.3 g of crude product were dissolved in a 25-fold amount of ethanol and treated with 1.1 equivalents of a saturated solution of fumaric acid in ethanol. There were obtained 1.2 g (49%) of 5,6,10,11-tetrahydro-3-methoxy-8-methyl-benzo[g]pyrazino[1,2-a]indole fumarate (1:1); m.pt.: 202°-203° C. (dec.).
