A process for the preparation of 9,10- dihydrolysergic acid esters.

PROCESS FOR THE PREPARATION OF 9,10-esters dihydrolysergic of formula (III), wherein R is alkyl C1-8 primary or secondary, (C2-4 alkenyl) -CH2, C3-8cycloalkyl or (C3-6cycloalkyl) C1-5 alkyl primary or secondary, not exceeding 8 TOTAL NUMBER OF carbon atoms; R1 is H, alkyl or allyl; And R2 is (C1-3 alkoxy) C5-7 cycloalkyl, C5-7cycloalkyl, C5-7cycloalkyl-O OTEC C3-7, C2-6 alkyl substituted with mono- or di (C1-3alkoxy) 4-hydroxycyclohexyl O . The process can be: A) esterifying a compound (V); B) oxidising a compound (VI), wherein R5 is a C3-6 hydroxyalkyl (-R9CH-R12), wherein R9 is H, CH3- C2H5- O and R12 is C2-5 ALKYL GROUP WITH SECONDARY -OH; C) alkylating a compound (III) wherein one of RO R1 is H; OD) hydrogenating a compound (VIII). The compounds (III) obtained are antagonists of serotonin, by blocking 5 HT2, BEING POTENTIALLY USEFUL FOR THE TREATMENT OF DISEASES WHICH IS THE MAIN CAUSE CURRENT excess serotonin.