Synthesis of fluorescent 4,6,8(14)-trien-3-one steroids via 3,5,7-trien-3-ol ethers. Important probes for steroid-protein interactions.

A general synthesis of fluorescent 4,6,8(14)-trien-3-one steroids with and without an aliphatic side chain is described via 3-alkoxy-3,5,7-trienes as intermediates. The advantages of this method are general applicability, good yields, limited number of reaction steps (up to four), and ready availability of starting materials (at low cost). a) Starting from ergosterol (1) or cholesta-5,7-dien-3-ol (2) and oxidizing them to ergosta-4,7,22-trien-3-one (3) or cholesta-4,7-dien-3-one (4) we synthesized the enol ethers (5) and (6). Subsequent treatment with DDQ gave the 4,6,8(14),22-tetraen-3-one (7) and the 4,6,8(14)-trien-3-one (8). b) Similarly 17 beta-(1-oxopropoxy)-androsta-4,6,8(14)-trien-3-one (13) was obtained, but the required enol ether was synthesized via the 4,6-dien-3-one (11).