Total Synthesis of (±)tanikolide

Asymmetric Synthesis of the Quinolizidine Alkaloid (−)-Epimyrtine with Intramolecular Mannich Cyclization and N-Sulfinyl δ-Amino β-Ketoesters

“…Sulfinimines were prepared as described earlier from ( R )-(−)- and ( S )-(+)- p -toluenesulfinamide; acetaldehyde or 5-benzyloxy pentanal ( 9 ); and Ti(OEt) 4 …”

“…Next, (−)- 7 was treated with TFA/MeOH and the reaction solution passed through a short plug of silica gel to remove the sulfinyl byproducts. The crude trifluoroacetate salt of 8 in MeOH afforded piperidine 10 on reaction with 1 equiv of 5-benzyloxy pentanal ( 9 ) in a 3:1 mixture of diastereoisomers and in 68% yield for the two steps. Decarboxylation with LiOH/MeOH or refluxing in HCl gave a single diastereomeric piperidine 11 in 25% yield.…”