Structure of a modified β-lactam analogue

4-[5-(2,2-Dimethyl-1,3-dioxolan-4-yl)-2,2-dimethyl-1,3-dioxolan-4-yl]-3-methoxy-1-(p-methoxy-phenyl)-2-azetidinone, C21H29NO7, M(r) = 378.23, monoclinic, P2(1), a = 14.024 (1), b = 10.288 (1), c = 15.912 (2) angstrom, beta = 107.2 (1)-degrees, V = 2192.8 (3) angstrom 3, Z = 4, D(m) = 1.123, D(x) = 1.115 g cm-3, lambda(Mo K-alpha) = 0.71073 angstrom, mu = 0.831 cm-1, F(000) = 872, T = 288 K, final R = 0.069 for 1575 observed reflections. There are two molecules in the asymmetric unit. The beta-lactam ring in both molecules is in a cis conformation and the N(1) atom in the beta-lactam ring is 0.004 angstrom away from the mean plane containing C(4), C(2) and C(12) in molecule 1, and 0.088 angstrom away from the similar mean plane in molecule 2. Of the two dioxolane rings in each of the two molecules in the asymmetric unit, one is in an envelope conformation and the other in a twisted conformation.