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Total Synthesis of (+)-1,2-Dehydroaspidospermidine, (+)-Condyfoline, and (–)-Tubifoline
TiCl3-Mediated Synthesis of 2,3,3-Trisubstituted Indolenines: Total Synthesis of (+)-1,2-Dehydroaspidospermidine, (+)-Condyfoline, and (−)-Tubifoline.
Angew. Chem. Int. Ed. 2020;
21 July 2020 (online)
Key wordsindole alkaloids - decarboxylative cross-coupling - 6π electrocyclization - 1,2-alkyl shift - retro-Mannich/Mannich reaction
Zhu and co-workers report the synthesis of 2,3,3-trisubstituted indolenines through a TiCl3-mediated reductive cyclization of tetrasubstituted alkenes bearing a 2-nitrophenyl substituent. An unprecedented sequence of reduction of nitroarene, 6π electrocyclization, 1,2-alkyl shift, and final nitrone reduction resulted in the syntheses of (+)-1,2-dehydroaspidospermidine, (+)-condyfoline, and (−)-tubifoline.
Palladium-catalyzed decarboxylative cross-coupling between enantioenriched vinyl triflate A and racemic potassium carboxylate B furnished cyclopentene C. Epoxidation, deprotection, and subsequent transannular epoxide ring opening provided E which was converted into (+)-1,2-dehydroaspidospermidine through reductive cyclization. Isomerization of (+)-condyfoline to (−)-tubifoline occurred by a retro-Mannich/Mannich reaction.