N-[2-(4,5-Dihydro-8-methoxy-1H-benzo[g]indol-1-yl)-ethyl]acetamide (4.7 g) was treated with 15 ml of phosphorus oxychloride under argon and the mixture was stirred at 50° C. for 30 minutes. The cooled mixture was added to 2000 g of ice-water and treated with 200 ml of 28% sodium hydroxide solution. The mixture was extracted once with 300 ml of methylene chloride and twice with 100 ml of methylene chloride each time, the organic phases were combined, dried with MgSO4 and freed from solvent. 4.2 g of residue were chromatographed on 250 g of aluminium oxide (neutral, III) with methylene chloride as the eluent. 3.8 g of crude product were dissolved in a 20-fold amount of hot ethanol and treated while hot with 1.1 equivalents of a saturated solution of fumaric acid in ethanol. There were obtained 4.7 g (84%) of 5,6,10,11-tetrahydro-2-methoxy-8-methylbenzo[g]pyrazino[1,2-a]indole fumarate (1:1); m.pt.: 175°-177° C. (dec.).
