Total synthesis indole core and side-chain modifications

2 Total Synthesis Indole Core and Side-Chain Modifications 

The Baran group has applied their innovative direct coupling strategy en route to acremoauxin A 07JACS12857 . In the event, indole coupling with camphorsultam propionate afforded excellent stereocontrol for establishing the requisite a-stereocenter in 136 

As many advances in indole side-chain modification are bom out of focused efforts in total synthesis, a vast amount of the literature has been devoted toward descriptions of tactics for controlled access to the polycyclic lattices that adorn the indole core. To that end, Williams 

A strategy for the synthsis of maleimides 141 has been reported that involves the Zn(OTf)2-catalyzed annulations of allenic esters 139 and isonitriles 140 070L4057 . Subsequent photoinduced ring closure of 141, followed by oxidative aromatization afforded the corresponding carbazole. 

In a final example, Coldham and co-workers have used an azomethine ylide strategy for constructing the tetracyclic ring system of 142, a precursor to iboga alkaloid deethylibophyllidine 07TL873 . In the event, condensation of indole C3-aldehyde and N-allyl glycine in refluxing toluene provided the requisite ylide dipole for cyclization onto a C2 tethered alkene. 

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