Enantio- and diastereocontrolled synthesis of (−)-19(S)-acetoxy-N1-acetyl-20-epitubifolidine

A Cascade Cycloaddition Strategy Leading to the Total Synthesis of (−)-FR182877

“…The suspected stereochemical relationship between FR182877 and hexacyclinic acid led us to target macrocycle 3 as a precursor common to both natural products. The pivotal transformations associated with both syntheses are the sequential transannular Diels–Alder (TADA)3a–3c and hetero‐Diels–Alder3d–3g cycloadditions (Scheme 1). Given the assumption that the transannular Diels–Alder reaction would be the initiating cycloaddition, the endo ‐ 3 transition state should afford the FR182877 skeleton while the diastereomeric exo ‐ 3 transition state should afford the hexacyclinic acid ring system.…”

A Cascade Cycloaddition Strategy Leading to the Total Synthesis of (−)-FR182877

“…The suspected stereochemical relationship between FR182877 and hexacyclinic acid led us to target macrocycle 3 as a precursor common to both natural products. The pivotal transformations associated with both syntheses are the sequential transannular Diels–Alder (TADA)3a–3c and hetero‐Diels–Alder3d–3g cycloadditions (Scheme ). Given the assumption that the transannular Diels–Alder reaction would be the initiating cycloaddition, the endo ‐ 3 transition state should afford the FR182877 skeleton while the diastereomeric exo ‐ 3 transition state should afford the hexacyclinic acid ring system.…”

Synthesis of Spirocyclic Indolenines

“…[147,148] These conditions were also employed by Banwell and co-workers to good effect in the synthesis of polycyclic framework 274. [149] An alternative to the DMTSF-mediated conditions was demonstrated by Ogasawara and co-workers, [150] using ac ombination of AgNO 3 and NCS in two step protocol, which was originally developed by Nicolaou and co-workersf or ar elated process. [151,152] Finally,H art and coworkers provided the sole example of an oxoniumi on reacting to form as pirocyclic indolenine;t he treatment of alcohol 277 with dimethoxymethane and ethylaluminumd ichloride is presumed to generate at erminal oxonium ion, which is attacked by nucleophilic indole C-3 position to form indolenine 278 in good overall yield.…”

“…Scheme38. Intramolecular addition to at hio/oxo-carbenium ion (Bosch et al; [143][144][145][146] ,Shibasaki et al; [147,148] Banwell et al; [149] Ogasawara et al; [150] Hart et al [153] ). sive range of spirocyclic indolenines 298 can be formed in good to excellenty ield.…”