Pd-Catalyzed Cross-Coupling Reaction of Sterically Hindered Vinyl Iodides and Organozinc Reagents. Synthesis of Vitamin D Analogues with an Aromatic Ring Attached at C-17

Abstract

Palladium-catalyzed coupling of steroid 17-iodo-6β-methoxy-3α,5-cyclo-5α-androst-16-ene (4) 17-iodoandrosta-5,16-dien-3β-ol (5), and structurally similar (3aS,7R,7aR)-benzenesulfonyl-3-iodo-3a-methyl-3a,4,5,6,7,7a-hexahydro-1H-indene (6) with various arylzinc chlorides, which were generated from aryl bromides 8 [1-bromomethylbenzene (8a), O-(triethylsilyl-2-bromophenyl)propan-2-ol (8b), 2-(4-bromophenyl)propan-2-ol (8c), 4-bromobenzonitrile (8d), 4-bromobenzoic acid methyl ester (8e), 4-bromobenzoic acid tert-butyl ester (8f) and 3-bromopyridine (8g)] via aryllihium derivatives (the Negishi coupling) was examined. The respective cross-coupling products were obtained in good yields for all aryl bromides except of 8c and 8e. Building blocks for synthesis of certain vitamin D analogues have been prepared.