text: The 1993 Keuhne synthesis concerns racemic strychnine. Starting compounds tryptamine 1 and 4,4-dimethoxy acrolein 2 were reacted together with boron trifluoride to acetal 3 as a single diastereomer in an amine-carbonyl condensation / sigmatropic rearrangement sequence.
  Hydrolysis with perchloric acid afforded aldehyde 4. A Johnson–Corey–Chaykovsky reaction (trimethylsulfonium iodide / n-butyllithium) converted the aldehyde into an epoxide which reacted in situ with the tertiary amine to ammonium salt 5 (contaminated with other cyclization products). Reduction (palladium on carbon/hydrogen) removed the benzyl group to alcohol 6, more reduction (sodium cyanoborohydride) and acylation (acetic anhydride / pyridine) produced 7 as a mixture of epimers (at C17). Ring closure of ring III to 8 was then accomplished with an aldol reaction using lithium bis(trimethylsilyl)amide (using only the epimer with correct configuration). Even more reduction (sodium borohydride) and acylation resulted in epimeric di-acetate 9.
  A DBU mediated elimination reaction formed olefinic alcohol 10 and subsequent Swern oxidation have an unstable amino ketone 11. In the final steps a Horner–Wadsworth–Emmons reaction (methyl 2-(diethy1phosphono)acetate) give acrylate ester 12 as a mixture of cis and trans isomers which could be coached into the right (trans) direction by application of light in a photochemical rearrangement, the ester group was reduced (DIBAL / boron trifluoride) to isostrychnine 13 and racemic strychnine 14 was formed by base-catalyzed ring closure as in the Woodward synthesis. 
  In the 1998 Keuhne synthesis of chiral (−)-strychnine the starting material was derived from chiral tryptophan.