Synthesis of triamcinolone acetonide-4-14C

The free hydroxyl groups in triamcinolone acetonide (1) were protected as silyl ethers to give the bis‐silyloxy derivative 4. Compound 4 was then hydrogenated over 5% palladium on carbon to give the Δ4‐3‐oxo steroid 5 which was then converted to the enol‐lactone 7 under selective reaction conditions. The enol‐lactone 7 was subjected to Grignard reaction with 14C‐methylmagnesium iodide to give an adduct 8a which on subsequent treatment with lithium 2,6‐di‐t‐butylphenoxide gave 4‐14C‐Δ4‐3‐oxo derivative 9. Compound 9. was heated with selenium dioxide in t‐butanol containing pyridine to give the Δ1,4‐3‐oxo derivative 10. Removal of the silyl protecting groups was readily accomplished by heating 10 with hydrochloric acid in methanol‐tetrahydrofuran solution to give the title compound 11.