Synthesis of ferrocene-substituted 2-azetidinones.
The photochemical reaction of alkoxychromium(0)carbene complexes and ferrocene mono- and disubstituted imines formed 2-azetidinones having one or two ferrocene moieties in good yields. Yields decrease when the carbene moiety bears an aminoferrocene moiety attached to the carbene carbon, while complex 9 having the ferrocene directly bonded to the carbene carbon was totally inert in these reactions. Access to beta-lactams with the ferrocene tethered to the C3 position through a methylene group was gained using the lithium enolate derived from ethyl 3-ferrocenylpropanoate. The reaction of this enolate produced two unexpected processes. Thus, 2-azetidinone 15 having an hydroxyl group at the C3 position was obtained together with the expected beta-lactam 14, by reaction of the lithium enolate of ethyl 3-ferrocenylpropenoate and imine 1. Additionally, unsaturated amide 17 was obtained by base-promoted Hoffmann-like breakage of the beta-lactam ring formed in the reaction of the same enolate and imine 2. Oxidation of the anion at the C3 of the 2-azetidinone ring on compound 14, as well as the sterically driven ring-breakage of the C3 anion derived from the nonisolated 2-azetidinone 18, should be responsible for this behavior.
Sierra
M A
MA
Departamento de Química Orgánica, Facultad de Química, Universidad Complutense, 28040-Madrid, Spain. sierraor@quim.ucm.es
Mancheño
M J
MJ
Vicente
R
R
Gómez-Gallego
M
M
D001384:Azetidines / Q000138:chemical synthesis*; D005296:Ferrous Compounds / Q000737:chemistry*; D007202:Indicators and Reagents; D007769:Lactams / Q000138:chemical synthesis*; D009682:Magnetic Resonance Spectroscopy; D000075163:Metallocenes; D010777:Photochemistry
D001384:Azetidines; D005296:Ferrous Compounds; D007202:Indicators and Reagents; D007769:Lactams; D000075163:Metallocenes; C004998:ferrocene