The reductocondensation of naltrexone (I) with N-methylbenzylamine (II) by means of sodium cyanoborohydride in THF gives the N-benzyl-N-methylaminomorphinan derivative (III), which is debenzylated by hydrogenation with H2 over Pd/C in methanol yielding the methylaminomorphinan (IV). Finally, this compound is acylated with 3(E)-(3-furyl)acryloyl chloride and NaOH, Na2CO3 or triethylamine in methanol, THF or chloroform. Alternatively, methylaminomorphinan (IV) can also be obtained by direct reductocondensation of naltrexone (I) with methylamine by means of H2 over PtO2 in methanol.