Abstract
AbstractUnique 9,13‐bridged D‐secoestrone alkaloids have been synthesized and structurally characterized. Treatment of 3‐methoxy‐16,17‐secoestra‐1,3,5(10)‐trien‐17‐al (6a) with aniline (7) or substituted aniline derivatives 8−28 in the presence of different Lewis and Brønsted acids produces the bridged azaestrone derivatives 51−67 and the alkenes 68−73 in high yields in a domino‐type process. The imines 29−50 are proposed as intermediates, undergoing 1,5‐hydride shifts via the iminium ion salts 75 to give the cations 77, which, depending on the substitution pattern on the aniline moiety, either afford the bridged compounds through a nucleophilic addition of the formed secondary amine to the benzylic carbocation or give the alkenes through the abstraction of a proton at C‐8. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
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