Resin catalysed ene reaction on 3β-toluene-p-sulfonoxy-(Z)-pregna-5,17(20)-diene: Synthesis of (20s)-6β-methoxy-3 α,5-cyclo-5α-pregnane-20-carboxyaldehyde

Article abstract of DOI:10.1016/S0040-4039(00)97031-X

Conversion of 17-keto steroid 2 in to 17(Z) ethylidene steroid 3 was achieved in high yields using a modified procedure. Ene reaction on 4 with paraformaldehyde in presence of acetic anhydride using various cation exchange resins as catalyst afforded stereo specifically the C-22 acetate 5 in excellent yields. For the first time cation exchange resins have been used as catalysts in ene reaction. Compound 5 was converted to C-22 aldehyde 1 using simple reaction sequence.