No abstract

Source of materialThe title compound was obtained from 2,3-O-ethandiyl-5,6-Oditosyl-L-ascorbic acid [1], which was allowed to react with 10 equiv. of NaN 3 in DMF for aperiod of 48 hat298 K. The reaction mixture was poured into water (273 K) and the product (60 % yield) was isolated by filtration. Experimental detailsAll hydrogen atomic positions were taken from adifference Fourier map. They were refined with variable isotropic displacement parameters. The value of the Flack parameter of 0.2(8) has no evidence, because the part of the anomalous dispersion is too small (Mo-source and C,H,N,O elements). In the figure, the displacement ellipsoids are shown at the 50 %probability level. Hydrogen atoms are shown in arbitrary size. DiscussionDerivatives of ascorbic acid with the two aliphatic hydroxy groups converted into leaving groups are known to exhibit highly regio-specific reactivity against nucleophiles (elimination at the CH-carbon atom and substitution at the CH 2 -carbon atom) [2][3][4].The title compound is in further support for this proposal. The crystal structure analysis exhibited a Z-configuration for the new C=C double bond, indicative of an anti-periplanar orientation of the reactive hydrogen atom and the para-tolylsulfonyl group in the transient state of the elimination reaction. As expected, the five membered lactone ring is virtually planar (the deviation of the five ring atoms O2/C3/C4/C7/C8 from their mean plane is less than 0.002 Å), whereas the six membered dioxa-cyclohexene ring (O4/C5/C6/O3/C7/C4) is considerably puckered and has a half-chair conformation (puckering parameters: Q =0.466(3) Å, q =129.2(3)°, j =88.2(3)°) [5].

cis-[CoL2](3+) (1a(3+)), trans-[CoL2](3+) (2a(3+)), cis-[Co(MeL)2](3+) (1b(3+)), and trans-[Co(MeL)2](3+) (2b(3+)), L = 1,4-diazepan-6-amine (daza) and MeL = 6-methyl-1,4-diazepan-6-amine (Medaza), were allowed to react as templates in acetonitrile with paraformaldehyde and triethylamine. Several Co(III) complexes, where two adjacent amino groups of two ligand moieties are interlinked by an oxidimethaneamine bridge, were obtained. Connection of a primary with a secondary amino group (prim-sec bridging) was found to be predominant. The singly and doubly bridged daza- and Medaza-derivatives 7a(3+), 9a(3+) and 7b(3+), 9b(3+) were characterized by crystal-structure analysis. The bridging process resulted in a slight lengthening of the mean Co-N distance, a red shift of the A1g-T1g transition, and an increase of the Co(III)/Co(II) reduction potential. Several minor components, which could be only partially separated by chromatographic methods, were also formed. The daza-derivatives 6a(3+) (prim-prim bridged) and 10a(3+) (bidentate coordination of one daza frame) formed in small quantities. The Medaza derivatives 3b(3+) and 4b(3+) (trans configuration of the Medaza frames, with additional pending carbinolamino groups), and 8b(3+) (with a methylideneimino group) represent intermediates of the condensation process. Their structure was again corroborated by X-ray diffraction. All bridged species (6a(3+), 7a(3+), 7b(3+), 8b(3+), 9a(3+), 9b(3+), and 10a(3+)) exhibited exclusively a cis orientation of the two diazepane frames, even if the trans configured 2a(3+) or 2b(3+) were used as starting materials. Molecular mechanics calculations indicate that in the bridged species with a trans configuration steric strain is substantially more pronounced. In alkaline aqueous media, 9a(3+) and 9b(3+) revealed a complete degradation of the bridges whereby the original 1a(3+) and 1b(3+) reformed. The pseudo-first-order rate constant k(obs) of the degradation reaction was found to depend linearly on OH(-) concentration. The degradation of the first bridge is about 100 times faster than the degradation of the second. The mechanism of formation and degradation of such oxidimethaneamine bridges is discussed.

No abstract