The present invention concerns processes for the preparation of each of the 4 diastereomers of formula (I) 1 in stereochemically pure form from either of two enantiomerically pure precursors. The tetracyclic ringsystem having trans-fused five and seven membered rings is formed in an acid-catalysed cyclization reaction. The invention further relates to the thus obtained cis-fused tetracyclic alcohol intermediates, the methanamine end-products, the methanamine end-products for use as a medicine, in particular as CNS active medicines.