Abstract A diastereoselective formal total synthesis of (±)??nephrosteranic acid (10) is described. The key step is to introduce the α??methylene group by the ozonolysis of monosubstituted alkenes followed by reaction with a preheated mixture of CH2Br2–Et2NH. The α??methyl group of compound 10 was formed from the reduction of the corresponding α?? methylene precursor.
