The effect of additives on the zinc carbenoid-mediated cyclopropanation of a dihydropyrrole.
J Org Chem
; 79(13): 6233-43, 2014 Jul 03.
Article
em En
| MEDLINE
| ID: mdl-24915024
The synthesis of a key intermediate in the preparation of oral antidiabetic drug Saxagliptin is discussed with an emphasis on the challenges posed by the cyclopropanation of a dihydropyrrole. Kinetic studies on the cyclopropanation show an induction period that is consistent with a change in the structure of the carbenoid reagent during the course of the reaction. This mechanistic transition is associated with an underlying Schlenk equilibrium that favors the formation of monoalkylzinc carbenoid IZnCH2I relative to dialkylzinc carbenoid Zn(CH2I)2, which is responsible for the initiation of the cyclopropanation. The factors influencing reaction rates and diastereoselectivities are discussed with the aid of DFT computational studies. The rate accelerations observed in the presence of Brønsted acid-type additives correlate with the minimization of the undesired induction period and offer insights for the development of a robust process.
Texto completo:
1
Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Pirróis
/
Zinco
/
Ciclopropanos
Idioma:
En
Revista:
J Org Chem
Ano de publicação:
2014
Tipo de documento:
Article