The title compound was prepared by two related ways. Reduction of pregn-4-ene (I) with sodium dithionite provided pregnane (II) with 5a-H configuration. Then, dehydrogenation with Pd(OAc)2 in refluxing acetonitrile gave pregn-1-ene (III). Cyclopropanation of (III) with dimethylsulfoxonium methylide (generated from trimethylsulfoxonium iodide and NaH in DMSO), yielded (IV). This was brominated with pyridinium tribromide, and the resulting 4-bromo compound (V) was dehydrobrominated by treatment with Li2CO3 and LiBr in DMF at 140 C to give the target compound. Alternatively, (I) was hydrogenated in the presence of Pd(OH)2 to afford pregnane (VI) with 5b-H configuration. The sequence of bromination with pyridinium tribromide, and elimination of the resulting bromide (VII) with Li2CO3 and LiBr provided pregn-1-ene (VIII), which was reduced to alcohol (IX) with NaBH4 in the presence of CeCl3 at 0 C. Insertion of carbene by means of a Simmons-Smith reaction with CH2I2 and Et2Zn yielded cyclopropane derivative (X), and this was again oxidized to ketone (XI) with Jones' reagent in acetone. Finally, the sequence of bromination and dehydro-bromination as before provided the target 4,5-unsaturated ketone.