From Tribromoacetic Acid

Owing to their structural complexity, Strychnos alkaloids, especially strychnine itself, are a benchmark in synthetic organic chemistry and have been prepared numerous times ]92]. Another alkaloid of the Strychnos family that enjoys increasing popularity nowadays is (+)-minfiensine. It was isolated from Strychnos minfimsis and features a l,2,3,4-tetrahydro-9a,4a-(iminoethano)-9H-carbazole motif, and hence is closely related to echitamine and vincorine [93]. A total synthesis of this beautiful structure was accomplished by MacMillan and coworkers [94]. Their key step was a highly efficient enantioselective domino Diels-Alder/isomerization/amine cycHzation reaction (Scheme 14.35). In this process, the chiral organocatalyst 226-TBA (TBA, tribromoacetic acid) was used, which reacted first with propargyl aldehyde 225 to form i minium ion 229 as intermediate, which underwent an endo-selective Diels-Alder reaction with 224... 

Dibromoketene can be generated from trimethylsilyl tribromoacetate (28) on treatment with Ph3P. Many other trihaloacetic acid derivatives undergo similar dehalogenation reactions. 

Figure 14 Separation of haloacetic acids and inorganic anions. Column Cryptand A15(x (150mm x 3mm) eluent gradient —8 to 3min, lOmM NaOH t = 3min, lOmM LiOH. Monochloro-cacetic (MCA), monobromoacetic (MBA), dichloroacetic (DCA), bromochloroacetic (BCA), dibromoacetic (DBA), trichloroacetic (TCA), monobromodichloroacetic (MBDCA), monochlorodibro-moacetic (MCDBA), and tribromoacetic (TBA) acids. (Reproduced from Ref. 64. Elsevier, 2008.)...

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