Level 1 – Case 1
6
In Summary
Although E-keto ester 2 seems to be an ideal substrate for a Knoevenagel cyclization, the expected product is not isolated when 2 is exposed to sodium ethoxide in
ethanol. Instead, products derived from two competitive pathways are observed.
The major product, bicyclic ester 4 is derived from a condensation involving the
cyclic enolate 11 and the minor product, tricyclic alcohol 5 comes from the oxidation of the already formed Knoevenagel product, which cannot be isolated.
Additional Comments
For other interesting surprises in the synthesis of guanacastepene A see Lin S,
Dudley GB, Tan DS, Danishefsky SJ (2002) Angew. Chem. Int. Ed. 41:2188-2191.
This problem is based on the work by Tan DS, Dudley GB, Danishefsky SJ
(2002) Angew. Chem. Int. Ed. 41:2185-2188.
Subjects of Revision
Knoevenagel and Claisen reactions.
6
In Summary
Although E-keto ester 2 seems to be an ideal substrate for a Knoevenagel cyclization, the expected product is not isolated when 2 is exposed to sodium ethoxide in
ethanol. Instead, products derived from two competitive pathways are observed.
The major product, bicyclic ester 4 is derived from a condensation involving the
cyclic enolate 11 and the minor product, tricyclic alcohol 5 comes from the oxidation of the already formed Knoevenagel product, which cannot be isolated.
Additional Comments
For other interesting surprises in the synthesis of guanacastepene A see Lin S,
Dudley GB, Tan DS, Danishefsky SJ (2002) Angew. Chem. Int. Ed. 41:2188-2191.
This problem is based on the work by Tan DS, Dudley GB, Danishefsky SJ
(2002) Angew. Chem. Int. Ed. 41:2185-2188.
Subjects of Revision
Knoevenagel and Claisen reactions.