Microwave assisted preparation of C(1)–C(11) oxygen-bridged pregnanes

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▸ Microwave irradiation induces hypoiodite type reactions with DIB/iodine. ▸ On sensitive substrates, photolysis with visible light is advantageously replaced by microwaves. ▸ Using microwave irradiation the 1α,11α-epoxy-4-pregnene was obtained in good yield. ▸ The stereochemical outcome of 1,11-bridge formation is explained by molecular modeling.

1,11-Epoxysteroids may be obtained by an intramolecular remote functionalization using Suarez reagent (diacetoxyiodobenzene/I2) and irradiation with visible light. We have found that photolysis with visible light may be advantageously replaced by microwave irradiation to prepare 1,11-oxygen bridges resulting in higher yields and shorter reaction times especially in the case of sensitive substrates. Both methodologies were compared on a set of representative 11-α-hydroxypregnanes (3, 8, 10 and 11).

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