Synthesis of beta-lactams by Ag+-induced ring expansion of 1-hydroxycyclopropylamines: a theoretical analysis.
A theoretical analysis of the silver-induced ring expansion of N-chloro-N-methyl-1-hydroxycyclopropylamine to form N-methyl-2-azetidinone, and of the Cl(-) elimination from this substrate without Ag(+) assistance, was performed using the B3LYP method and the 6-31+G(d) basis set for C, N, O, H, and Cl atoms and the relativistic effective core pseudopotential LANL2DZ complemented with one set of f polarization functions (zeta(f) = 0.473) for the Ag atom. The partial Ag(+)-assisted extrusion of Cl(-) at the rate-determining transition state provokes an important change in the nodal properties of the frontier molecular orbitals of the H(3)CClNCOHAg(+) fragment, thus making very stabilizing HOMO-LUMO interactions between this fragment and the C(2)H(4) moiety possible. This interaction leads to the ring opening and release of most of the strain energy, giving rise to a low energy barrier for the process. Also, by assisting the Cl(-) extrusion, Ag(+) avoids the elimination of the hydroxyl hydrogen atom, which would provoke the fragmentation of the system instead of the formation of the beta-lactam.
Campomanes
Pablo
P
Departamento de Química Física y Analítica, Facultad de Química, Universidad de Oviedo, Julian Clavería, 8, 33006 Oviedo, Principado de Asturias, Spain.
Menéndez
M Isabel
MI
Cárdenas-Jirón
Gloria I
GI
Sordo
Tomás L
TL
D003521:Cyclopropanes / Q000737:chemistry*; D012834:Silver / Q000737:chemistry*; D047090:beta-Lactams / Q000138:chemical synthesis*
D003521:Cyclopropanes; D047090:beta-Lactams; D012834:Silver; C067351:cyclopropylamine