Chiral Brønsted Base Activation of Donor-Acceptor Cyclopropanes toward Diastereo- and Enantioselective [3 + 2] Cycloaddition with Isatin-Derived Ketimines.
J Org Chem
; 89(12): 8691-8705, 2024 Jun 21.
Article
in En
| MEDLINE
| ID: mdl-38856011
ABSTRACT
Organocatalyzed diastereo- and enantioselective [3 + 2] cycloaddition reactions of donor-acceptor (D-A) cyclopropanes with isatin-derived ketimines are presented. Different from well-developed Lewis acid activation protocols which promote the reactivity of D-A cyclopropanes through coordinating to the acceptor group, in this reaction, dicyanocyclopropylmethyl ketones can be activated through nucleophilic activation of the donor group by using dihydroquinine-derived squaramide as Brønsted base catalyst. The reaction affords functionalized spiro[oxindole-3,2'-pyrrolidines] with two nonadjacent tetra- and tri-substituted stereocenters in 83-99% yields, moderate to excellent diastereoselectivities (up to >201 diastereomeric ratio (dr)), and excellent enantioselectivities (up to >99% enantiomeric excess (ee)) under mild conditions.
Full text:
1
Collection:
01-internacional
Database:
MEDLINE
Language:
En
Journal:
J Org Chem
Year:
2024
Type:
Article
Affiliation country:
China