The conversion of lactones to ortho esters has been accomplished by treatment with epoxides in the presence of boron trifluoride (1) or with triethyloxonium fluoroborate followed by sodium et&oxide. (2) We have recently found that ketalization of steroidal ketones containing a lactone group also resulted in reaction of the la&one with ethylene glycol. The resultant ortho esters are readily cleaved to the starting la&ones. A mixture of 1, (3) ethylene glycol and a catalytic amount of _p-toluenesulfonic acid in benzene solution was refluxed for 66 hours with continuous removal of water to afford 2 (4) (72% yield): mp 195-197'; nmr (CDC13) 6 3.9-4.3 (m, 4H), mass spectrum (low resolution) m/e 428 (&). The infrared spectrum of 2 exhibited no carbonyl band. Treatment of 1 (5) under the above conditions gave 3 (56% yield): mp 163-164"; nmr (CDC13) 6 3.8-4.2 (m, 4H), mass spectrum (low resolution) 9, 350 (M+). Cleavage of the ortho esters 2 and 3 to the starting lactones proceeded readily using anhydrous magnesium sulfate in wet benzene as described (6) for the cleavage of A 4 -3-ethyleneketals. Steric hindrance is apparently crucial in the ortho ester formation since 17a-oxo-D-homo-1,4-androstadiene-3,17_dione (7) did not react with ethylene glycol under the above conditions. Monocyclic lactones such as y-butyrolactone are opened under the reaction conditions and do not give ortho esters.