the presence of cerium iii salts the resulting product 2a r 3 u2550 h r 4 u2550 r 5 u2550 oh which is the epimer at the 10 position of 3 is suitably protected at the 7 and 10 positions and used for the synthesis of taxanes 1a str7 the new secotaxane 5 is obtained as a by product of the reaction sequence given in scheme 1 str8 secotaxane 5 can be used for the synthesis of further taxanes with potential anti tumoural activity the present invention also relates to novel secotaxane skeleton derivatives prepared by semisynthesis and having a powerful anti tumoural activity these derivatives have formula 5a str9 wherein r 1 and r 2 which can be the same or different are a c 1 c 20 alkyl c 2 c 8 alkenyl aryl preferably phenyl or heteroaryl groups r 2 can also be tert butoxy taxanes of formula 5a are prepared by esterificating compound of formula 5 in position 13 using the suitably activated isoserine chains as acylating agents as reported in literature for the semisynthesis of taxol and analogues thereof see for example ep a 400 971 e didier et al tetrahedron letters 35 2349 1994 e didier at al ibid 35 3063 1994 the hydroxy groups.