Contribution of the anomeric effect to the solution and crystal structure of [1S,2S,6S,7s]-1,6-diaza-4,9-dioxa-2,7-dimethoxycarbonylbicyclo[4.4.1]undecane, a condensation product of L-serine methyl ester with formaldehyde.
The reaction of L-serine methyl ester hydrochloride (1) with paraformaldehyde (2) in dichloromethane in the presence of triethylamine afforded a novel compound: [lS,2S,6S,7S]-1,6-diaza-4,9-dioxa-2,7-dimethoxycarbonylbicyclo[4.4.1]undecane (4) as a 2:3 adduct of 1 with 2. 1H and 13C NMR spectroscopy were unable to discriminate between two possible symmetrical structures. The latter was unambiguously proved by X-ray crystallography. The crystal structure established: (i) the existence of two identical seven-membered rings each containing a N-C-O grouping; (ii) the existence of a long C-O-C-N-C-N-C-O-C sequence in which each nitrogen belongs simultaneously to a N-C-O (oxazolidine) and to a N-C-N (aminal) motifs; (iii) the existence of a chair-like conformation for both seven-membered rings; (iv) the antiperiplanar geometry of pN-C-O and consequently the manifestation of a strong anomeric effect in both N-C-O groupings, whereas anomeric effect was virtually absent in the N-C-N sequence, as corroborated by bond distances and bond angles. Chemical shifts, coupling constants and NOE effects confirm that the conformational features of 4 are preserved in solution.
Sélambarom
J
J
Laboratoire de Chimie Organique, Universite de Montpellier II, France.
Monge
S
S
Carré
F
F
Fruchier
A
A
Roque
J P
JP
Pavia
A A
AA
D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000737:chemistry*; D018360:Crystallography, X-Ray; D003998:Dicarboxylic Acids / Q000737:chemistry*; D005557:Formaldehyde / Q000737:chemistry*; D015394:Molecular Structure; D019906:Nuclear Magnetic Resonance, Biomolecular; D012694:Serine / Q000031:analogs & derivatives / Q000737:chemistry*; D012996:Solutions; D013237:Stereoisomerism
C429010:1,6-diaza-4,9-dioxa-2,7-dimethoxycarbonylbicyclo(4.4.1)undecane; D019086:Bridged Bicyclo Compounds, Heterocyclic; D003998:Dicarboxylic Acids; D012996:Solutions; D005557:Formaldehyde; D012694:Serine; C429009:serine methyl ester