134706-56-2Relevant academic research and scientific papers
Stereoelectronically Controlled Cyclization Reactions on the Way to peri-Fused Tetrahydropyrazolopyridines as Aza Analogs of Ergoline Partial Structures
Gmeiner, Peter,Sommer, Josef
, p. 921 - 927 (2007/10/02)
The synthesis of the 3-substituted tetrahydropyrazolopyridin-4-ylalkyl iodides 7a, 7b, 8a and 8b as well as their behavior towards anionic cyclization conditions have been investigated.An (enol endo)-exo-tet-type ring closure only proceeds when a seven-membered ring is annulated (9b, 10b).Otherwise, treatment of the β-keto ester 7a with NaH results in O-alkylation to yield the stereoelectronically favored (Z)-enol ether 13a, which can be isomerized to the thermodynamically more stable (E) isomer 13b.Various attemps to achieve ring closure of the methyl ketone 8a failed; instead, β-elimination is observed.Annulation of a six-membered carbocycle is achieved when the triester 17 is treated by a Dieckmann condensation to give the tricyclic products 18 and 19.
