In this contribution, we provide a comprehensive overview of acyclic twisted amides, covering the literature since 1993 (the year of the first recognized report on acyclic twisted amides) through June 2020. The review focuses on classes of acyclic twisted amides and their key structural properties, such as amide bond twist and nitrogen pyramidalization, which are primarily responsible for disrupting nN to π*C═O conjugation. Through discussing acyclic twisted amides in comparison with the classic bridged lactams and conformationally restricted cyclic fused amides, the reader is provided with an overview of amidic distortion that results in novel conformational features of acyclic amides that can be exploited in various fields of chemistry ranging from organic synthesis and polymers to biochemistry and structural chemistry and the current position of acyclic twisted amides in modern chemistry.

Acyclic Twisted Amides.

A new lanthanide citrate coordination polymer [Dy(citrate)(H2O)]n (1) was hydrothermally synthesized and structurally characterized by elemental analyses, single-crystal X-ray diffraction, IR spectroscopy, thermogravimetric analysis, photoluminescence spectrum, and magnetic measurements. The structure of 1 exhibits a 2D layer structure, in which the Dy2O2 dimer serves as the building block. The photoluminescence spectrum shows blue luminescence in the solid state at room temperature. Owing to the special frustration structure, unusual magnetic relaxation was found in compound 1. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Unusual Magnetic Behavior of a 2D Citrate‐Bridged Dysprosium(III) Coordination Polymer

Synthesis and characterization of a (+)-catechin and L-(+)-ascorbic acid cocrystal as a new functional ingredient for tea drinks

The structures and chemistry of 1,3-oxazine derivatives and their carbo- or heterocycle-fused analogs have been studied thoroughly from various aspects in recent decades. Numerous methods have been devised for the preparation of the variously saturated or substituted derivatives of this family of heterocycles, and are discussed in this chapter with regard to the mode of assembly of the ring atoms. The latest developments in these fields, involving multicomponent reactions, solid-phase procedures, and both conventional and enzymatic catalytic methods of synthetic organic chemistry, allow the highly regio-, stereo-, and enantioselective preparation of these compounds. With the increasing demand for chiral nonracemic molecules, stereoselective methods for the synthesis of 1,3-oxazine derivatives and applications of enantiopure 1,3-oxazines in asymmetric transformations have recently gained in importance. The wide-ranging possibilities for the application of 1,3-oxazine derivatives in organic syntheses have been utilized in the preparation of numerous mono- or difunctional compounds, including key intermediates toward natural products or bioactive substances. Besides the structural and chemical characterization of 1,3-oxazines and their carbo- or heterocycle-fused analogs, their most important biologically active derivatives are also discussed.

1,3-Oxazines and their Benzo Derivatives

Synthesis of new beta-lactams is an attractive field because some of these types of molecules are biologically active. The design and preparation of C4-nitrogen-substituted beta-lactams are not known. Structurally diverse C4-N-substituted beta-lactams can be synthesized efficiently from amidines. Amidines are obtained by reacting beta-cyano ester and secondary amine in the presence of a promoter. Amidines can then be used for the preparation of novel beta-lactams through well-known reactions. Bismuth, indium, and copper salts can be used as the promoter to undergo nucleophilic reactions. Several new reactions are here identified with amidines in high yield for the synthesis of unique monocyclic to polycyclic beta-lactams. Some of these compounds are optically active with diverse groups at different positions of the ring system.

Hypotheses for synthesis of novel chiral beta-amino-beta-lactams through amidines

In the title compound, C17H20BrNO3, synthesized from spiro­[2H-1,3-benzoxazine-2,1′-cyclo­hexan]-4(3H)-one and 2-bromo­butanoyl bromide, the chair cyclohexane ring in the mol­ecule shows high asymmetric induction in the synthesis of trans β-lactams.

3‐(2‐Bromo­butano­yl)spiro­[2H‐1,3‐benzoxazine‐2,1′‐cyclo­hexan]‐4(3H)‐one

The title compound, C20H17FO7·C3H6O, is a potential antitumour agent. Its absolute configuration was assigned based on that of the synthetic precursor. Intermolecular O—H⋯O hydrogen bonds link the mol­ecules in the crystal structure into layers parallel to (010). These layers are stabilized by weak interlayer C—H⋯O hydrogen bonds.

(5R,5aR,8aR,9S)-5-(3,4-dihydroxy-5-methoxyphenyl)-9-fluoro-5,8,8a,9-tetrahydrofuro[3′,4′:6,7]naphtho[2,3-d]-1,3-dioxol-6(5aH)-one acetone solvate

The title compound, C30H31ClN2O4, crystallizes as discrete mol­ecules Non-classical C—H·O hydrogen bonds link the mol­ecules in the crystal structure into a sheet parallel to (01)

3-[(2R*,3S*)-3-(4-Chlorophenyl)-3-(2-methoxyanilino)-2-methylpropionyl]spiro[2H-1,3-benzoxazine-2,1′-cyclohexan]-4(3H)-one

An efficient and enantioselective synthesis of trans-β-lactams from carboximide 1 and imines 2 using a chiral auxiliary under the classical Reformatsky reaction conditions is described. An enolate-imine mechanism has been proposed for this reaction.

Enantioselective Synthesis of β-Lactams Using a Chiral Auxiliary

The title compound, C22H26N3O, crystallizes in space group P21 with two mol­ecules in the asymmetric unit. Intermolecular N—H⋯O hydrogen bonds play an important role in the formation of polymeric chains running along the crystallographic a axis.

Shan-Zhong Jian

Papers

3‐(2‐Bromobutanoyl)spiro[2H‐1,3‐benzoxazine‐2,1′‐cyclohexan]‐4(3H)‐one

(5R,5aR,8aR,9S)-5-(3,4-dihydroxy-5-methoxyphenyl)-9-fluoro-5,8,8a,9-tetrahydrofuro[3′,4′:6,7]naphtho[2,3-d]-1,3-dioxol-6(5aH)-one acetone solvate

3-[(2R,3S)-3-(4-Chlorophenyl)-3-(2-methoxyanilino)-2-methylpropionyl]spiro[2H-1,3-benzoxazine-2,1′-cyclohexan]-4(3H)-one

Enantioselective Synthesis of β-Lactams Using a Chiral Auxiliary

4‐(9‐Acridin‐9‐ylamino)‐2,2,6,6‐tetramethylpiperidine N‐oxide

Shan-Zhong Jian

Papers

3‐(2‐Bromo­butano­yl)spiro­[2H‐1,3‐benzoxazine‐2,1′‐cyclo­hexan]‐4(3H)‐one

(5R,5aR,8aR,9S)-5-(3,4-dihydroxy-5-methoxyphenyl)-9-fluoro-5,8,8a,9-tetrahydrofuro[3′,4′:6,7]naphtho[2,3-d]-1,3-dioxol-6(5aH)-one acetone solvate

3-[(2R*,3S*)-3-(4-Chlorophenyl)-3-(2-methoxyanilino)-2-methylpropionyl]spiro[2H-1,3-benzoxazine-2,1′-cyclohexan]-4(3H)-one

Enantioselective Synthesis of β-Lactams Using a Chiral Auxiliary

4‐(9‐Acridin‐9‐yl­amino)‐2,2,6,6‐tetra­methyl­piperidine N‐oxide

3‐(2‐Bromobutanoyl)spiro[2H‐1,3‐benzoxazine‐2,1′‐cyclohexan]‐4(3H)‐one

3-[(2R,3S)-3-(4-Chlorophenyl)-3-(2-methoxyanilino)-2-methylpropionyl]spiro[2H-1,3-benzoxazine-2,1′-cyclohexan]-4(3H)-one

4‐(9‐Acridin‐9‐ylamino)‐2,2,6,6‐tetramethylpiperidine N‐oxide