ml of a solution of 2M n-butyllithium in hexane were added at 5° C over 15 minutes to a solution of g of tertbutylmethyl sulfoxide in 70 ml of tetrahydrofuran and after 10 minutes, g of the product of Step A in 20 ml of tetrahydrofuran were added thereto. The temperature of the mixture returned to room temperature to obtain a limpid solution which was stirred overnight. The mixture was poured into an ice-water mixture and was extracted with methylene chloride. The extracts were washed with water, dried over sodium sulfate and evaporated to dryness to obtain g of product. The latter was dissolved in 70 ml of acetone and 10 ml of 2N hydrochloric acid. After 15 minutes, the mixture was diluted with water and was vacuum filtered to obtain g of a mixture of isomers. The product was chromatographed over silica and was eluted with an 80-20 chloroform-acetone mixture to obtain g isomer A of (17R) 7α-methyl-21-tertbutylsulfinyl-Δ 4 -(17α)-pregnene-17-ol-3-one melting at 270° C after crystallization from a methylene chloride-methyl ethyl ketone and a specific rotation [α] D 20 = -° ± ° (c = % in chloroform) and then g of isomer B of (17R) 7α-methyl-21-tertbutylsulfinyl-Δ 4 -(17α)-pregnene-17-ol-3-one melting at 248° C after crystallization from a methyl ethyl ketone-isopropyl ether mixture and a specific rotation [α] D 20 =+° ± 2° (c = % in chloroform).