Structural investigation on isomeric spiro-β-lactams: NMR and X-ray study

Abstract

Two diastereoisomers of 1,4-diphenyl-4-methulthio-3(4′)spiro-(2′,2′)-dimethyl-5′-methoxy-carbonyl-1′,3′-dioxolane)-2-azetidinone have been synthesized and investigated by 1H and 13C NMR, and structural X-ray diffraction methods. The isomer 3( SR), 4( RS), 5( RS) ( I) crystallizes in a triclinic system, space group P 1 , with cell dimendions α = 9.000(4), b = 9.606(2), c = 13.861(2) Å, α = 104.44(2)°; β = 107.06(2)°, γ = 100.28(3)° and Z = 2; the isomer 3( RS), 4( RS), 5( RS) ( II) crystallizes in a monoclinic system, space group P2 1/ n, with cell dimensions α = 9.642(1), b = 33.631(4), c = 12.967(1) Å, β = 96.766(8)° and Z = 8. Both structures were solved by direct methods and refined by a full-matrix, least-squares procedure to give R = 0.0670 and 0.0422 for I and II, respectively. A close investigation of the molecular geometrical parameters of I and II confirmed all the conclusions drawn from NMR (nuclear Overhauser effect) experiments.