| abstract |
The invention relates to a method for the preparation of a steroid-derived ketal according to general formula I: wherein R1 is CH3 or C2H5; R2 is OH; R3 is H, CH3; C = _CH, CH2Hal, or CH2CN; or R2 and R3 are together O; R4 is alkylene (2 to 5 carbon atoms); and Hal is Cl, Br or I, characterized in that the compound of formula II: where R1, R2, and R3 have the meanings given above, is treated in the presence of an orthoester of formula III: or an orthoester of the formula IV: where R4 has the meaning indicated above, or a mixture thereof, with an alcohol according to the general formula HOR4OH, where R4 has the meaning given above. |