The first enantioselective total-synthesis of the melodinus-alkaloid (+)-meloscine is described. As the key step, a hydrogen bond mediated, template-controlled, enantioselective intermolecular [2+2]-photocycloaddition was for the first time employed in natural-product synthesis. Further transformations include a retro-benzilic ester rearrangement of the initial photoproduct, a three-fold domino-reaction with an intramolecular reductive amination, a Johnson-Claisen rearrangement and a ring-closing metathesis. The synthesis uses 15 linear steps with an overall-yield of 7% and also allows for the first multi-gram synthesis of the pentacyclic melodan carbon skeleton. In addition, a novel type of photochemical radical-cyclization, a photochemical oxidation using atmospheric oxygen and the reductive cleavage of annelated cyclobutanes to eight-membered lactams were investigated.
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The first enantioselective total-synthesis of the melodinus-alkaloid (+)-meloscine is described. As the key step, a hydrogen bond mediated, template-controlled, enantioselective intermolecular [2+2]-photocycloaddition was for the first time employed in natural-product synthesis. Further transformations include a retro-benzilic ester rearrangement of the initial photoproduct, a three-fold domino-reaction with an intramolecular reductive amination, a Johnson-Claisen rearrangement and a ring-closin...
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