The synthesis of strophasterols C, E, and F has been accomplished from a 14,15-secoergostane derivative via a 1,3-dipolar cycloaddition of a nitrile oxide intermediate to simultaneously install an isolated cyclopentane ring and a C23 oxygen functionality in a diastereoselective manner and a regio- and diastereoselective selenohydroxylation of an olefinic intermediate under thermodynamic conditions. This synthesis also enabled the stereochemical confirmation of strophasterol C.