Minfiensine Overman synthesis

This chapter is based on an approach by Overman and coworkers who completed the first enantioselective total synthesis of (+)-minfiensine (1) in 2005. ... 

Minfiensine (99) was first synthesized by Overman and coworkers in 2005 [48] (Scheme 19). Their synthesis commenced with acid-catalyzed transamination of... 

Scheme 19 Total synthesis of minfiensine (99) by Overman and coworkers...

Dounay AB, Overman LE, Wrobleski AD (2005) Sequential catalytic asymmetric Heck-iminium ion cyclization enantioselective total synthesis of the Strychnos alkaloid minfiensine. J Am Chem Soc 127 10186-10187... 

In 2005, the Overman group reported the first total synthesis of minfiensine... 

In another beautiful application, Overman et al. developed the total synthesis of the natural product (+)-minfiensine (130), having a l,2,3,4,-tetrahydro-9a,4a-(iminoethano)9H-carbazol core (Scheme 7.29) [80]. The key step in their synthesis is a tandem process consisting of a catalytic asymmetric Mizoroki-Heck ring closure and an N-acyliminium ion cyclization of dienyl carbamate triflate 127 (127—>128). The reaction proceeded smoothly using the Pfaltz ligand (S)- Bu-PHOX (85), providing (dihydroiminoethano)carbazole 129 after the addition of excess trifluoroacetic acid, with 75% overall yield and 99% enantiomeric purity (127 129). 

One additional example of forming a quarternary stereocenter in alkaloid total synthesis by using a catalytic asymmetric Heck reaction was reported in 2005 by Overman et al. The complex indole alkaloid minfiensine 33 exhibits impressive biological activities (Scheme 13.9). It was... 

Minfiensine, a secoiridoid indole alkaloid, was isolated from the African plant Strychnos minfiensis by Massiot and co-workers in 1989. The unique structure feature of the 1,2,3,4-tetrahydro-9a,4a-(iminoethano)-9//-carbazole has received much attention for the synthetic efforts and has culminated in several elegant total syntheses. For example. Overman et al. reported on the first and second total synthesis of (-l-)-minfiensine. " In addition, Qin et al. revealed a synthesis of ( )-minfiensine in 2008. Recently, MacMillan and co-workers reported on a nine-step enantiose-lective total synthesis of (-l-)-minfiensine via the key step reaction of organocatalytic Diels-Alder cyclization and amine heterocyclization cascade (Scheme 21.32). For the key step reaction in their approach, reaction of 2-vinylindole 139 and 3 equivalents of propynal in the presence of secondary amine catalyst 140 followed by the addition of NaBH4, stereoselective afforded the tricyclic alcohol 142 via a iminium activated endo-selectiye Diels-Alder cycloaddition and a 5-exo amine heterocy cliz ation. 

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