Weak C-H…O and C-H…π hydrogen bonds and π-π stacking interactions in a series of four -N'-[(E)-(aryl)methylidene]- -methyl-2-oxo-1,3-oxazolidine-4-carbohydrazides

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Abstract

Oxazolidin-2-ones are widely used as protective groups for 1,2-amino alcohols and chiral derivatives are employed as chiral auxiliaries. The crystal structures of four differently substituted oxazolidinecarbohydrazides, namely N‘-[(E)-benzyl­idene]-N-methyl-2-oxo-1,3-oxazolidine-4-carbohydrazide, C₁₂H₁₂N₃O₃, (I), N‘-[(E)-2-chloro­benzyl­idene]-N-methyl-2-oxo-1,3-oxazolidine-4-car­bohydrazide, C₁₂H₁₂ClN₃O₃, (II), (4S)-N‘-[(E)-4-chloro­benzyl­idene]-N-methyl-2-oxo-1,3-oxazolidine-4-carbohydrazide, C₁₂H₁₂ClN₃O₃, (III), and (4S)-N‘-[(E)-2,6-di­chloro­benzyl­idene]-N,3-dimethyl-2-oxo-1,3-oxazolidine-4-carbohydrazide, C₁₃H₁₃Cl₂N₃O₃, (IV), show that an unexpected mild-condition racemization from the chiral starting materials has occurred in (I) and (II). In the extended structures, the centrosymmetric phases, which each crystallize with two mol­ecules (A and B) in the asymmetric unit, form A+B dimers linked by pairs of N-HO hydrogen bonds, albeit with different O-atom acceptors. One dimer is composed of one mol­ecule with an S configuration for its stereogenic centre and the other with an R configuration, and possesses approximate local inversion symmetry. The other dimer consists of either R,R or S,S pairs and possesses approximate local twofold symmetry. In the chiral structure, N-HO hydrogen bonds link the mol­ecules into C(5) chains, with adjacent mol­ecules related by a 2₁ screw axis. A wide variety of weak inter­actions, including C-HO, C-HCl, C-H and – stacking inter­actions, occur in these structures, but there is little conformity between them.

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Keywords: oxazolidine ring; carbohydrazide; racemic; crystal structure; weak hydrogen bonds.Document Type: Research ArticleDOI: https://doi.org/10.1107/S2053229615012450Publication date: 07 de Julho de 2015[:en]

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Abstract

Oxazolidin-2-ones are widely used as protective groups for 1,2-amino alcohols and chiral derivatives are employed as chiral auxiliaries. The crystal structures of four differently substituted oxazolidinecarbohydrazides, namely N‘-[(E)-benzyl­idene]-N-methyl-2-oxo-1,3-oxazolidine-4-carbohydrazide, C₁₂H₁₂N₃O₃, (I), N‘-[(E)-2-chloro­benzyl­idene]-N-methyl-2-oxo-1,3-oxazolidine-4-car­bohydrazide, C₁₂H₁₂ClN₃O₃, (II), (4S)-N‘-[(E)-4-chloro­benzyl­idene]-N-methyl-2-oxo-1,3-oxazolidine-4-carbohydrazide, C₁₂H₁₂ClN₃O₃, (III), and (4S)-N‘-[(E)-2,6-di­chloro­benzyl­idene]-N,3-dimethyl-2-oxo-1,3-oxazolidine-4-carbohydrazide, C₁₃H₁₃Cl₂N₃O₃, (IV), show that an unexpected mild-condition racemization from the chiral starting materials has occurred in (I) and (II). In the extended structures, the centrosymmetric phases, which each crystallize with two mol­ecules (A and B) in the asymmetric unit, form A+B dimers linked by pairs of N-HO hydrogen bonds, albeit with different O-atom acceptors. One dimer is composed of one mol­ecule with an S configuration for its stereogenic centre and the other with an R configuration, and possesses approximate local inversion symmetry. The other dimer consists of either R,R or S,S pairs and possesses approximate local twofold symmetry. In the chiral structure, N-HO hydrogen bonds link the mol­ecules into C(5) chains, with adjacent mol­ecules related by a 2₁ screw axis. A wide variety of weak inter­actions, including C-HO, C-HCl, C-H and – stacking inter­actions, occur in these structures, but there is little conformity between them.

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Keywords: oxazolidine ring; carbohydrazide; racemic; crystal structure; weak hydrogen bonds.Document Type: Research ArticleDOI: https://doi.org/10.1107/S2053229615012450Publication date: 07 de Julho de 2015[:]