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The cyclohexene ring that constitutes a part of the tetrahydroxanthene fused-ring system of the title compound, C23H26O4, adopts a flattened half-chair conformation that approximates an envelope conformation (in which the methylene C atom bearing the two methyl substituents represents the flap) as five of the six atoms lie approximately on a plane (r.m.s. deviation = 0.020 Å). The mean plane of the cyclohexene ring with the hydroxy substituent is approximately perpendicular to the mean plane of the tetrahydroxanthene system. In the crystal, adjacent molecules are linked by O—H...Ocarbonyl hydrogen bonds into a chain running along the b axis.

The Cu(II) atom in the title compound, [Cu(C(12)H(11)N(2)O(4))(2)(C(10)H(14)N(2)O)(H(2)O)](n), lies in a square plane defined by the O atoms of the carboxyl-ate ions, the N atom of the N-heterocycle and the water mol-ecule. Coordination by an amido O atom of an adjacent N-heterocycle in the apical direction leads to a polymeric chain running along [01[Formula: see text]]. The chain motif is consolidated by hydrogen bonds involving the water mol-ecule; the water mol-ecule is a hydrogen-bond donor to the free carbonyl atoms of the carboxyl-ate ions. Intra-molecular N-H⋯O hydrogen bonds also occur.

The complete molecule of the title compound, C28H38O2, is generated by a crystallographic centre of symmetry. The molecular conformation displays an intramolecular C—H...π interaction.

In the title compound, C17H19NO5, the cyclohexene ring is in a half-chair conformation and the isoxazole ring in an envelope conformation with the N atom as the flap. The C atoms in the 4- and 6-positions are of the same absolute configuration, whereas the C atom in the 5-position is of the opposite configuration, i.e. (4S*,5R*,6S*). The methyl fragment of the ethoxycarbonyl group at position 5 is disordered over two sets of sites in a 0.60:0.40 ratio. The crystal packing displays intermolecular N—H...O and O—H...O hydrogen bonds.

In the title compound, C6H12N2O2S, the heterocyclic ring has a sofa conformation. The molecular conformation is stabilized by an intramolecular O—H...O hydrogen-bond interaction with graph-set motif S(6). In the crystal, molecules are linked by O—H...S, N—H...S and N—H...O hydrogen-bond interactions, forming an extended two-dimensional framework parallel to the ac plane.

The title compound, [K(C(17)H(18)NO(5))](n), reveals the relative configuration (4R*,5S*,6R*) whereas its crystals are racemic. The cyclo-hexane ring adopts a half-chair conformation and the isoxazole ring has an envelope conformation. The ethyl fragment of the eth-oxy-carbonyl group at position 5 is disordered in a 0.547 (7):0.453 (7) ratio. The K(+) ion is surrounded by five O atoms from three ligands at distances ranging from 2.606 (2) to 3.028 (2) Å, generating a three-dimensional network. The crystal packing displays inter-molecular O-H⋯N and O-H⋯O hydrogen bonds in which the hy-droxy group acts as a double proton donor.

In the title compound, C16H25NO, the N-tert-butylpropanamide fragment is essentially planar, with the exception of two C atoms of the tert-butyl group (r.m.s. deviation = 0.005 Å), forming a dihedral angle of 84.09 (10)° with the plane of the mesityl fragment (r.m.s. deviation = 0.002 Å). The crystal packing is stabilized by an intermolecular N—H...O hydrogen bond, which links the molecules into chains with graph-set notation C(4) running parallel to the c axis.

The six-membered oxacyclohexene ring of the title compound, C13H14N2O2S, is fused with the benzene ring and the quarternary C atom lies above the plane of the benzene ring by 0.229 (8) Å, whereas the methine C atom (which bears the acetyl substituent) lies below this plane by 0.595 (8) Å. The oxacyclohexene ring is also fused with the sofa-shaped 2,6-diazacyclohexanone ring. The methine C atom that belongs to both six-membered rings lies above the mean plane of the other five atoms (r.m.s. deviation = 0.077 Å) by 0.759 (5) Å. In the crystal, N—H...S hydrogen bonds link adjacent molecules into a linear chain.

The title compound, C17H20N2O2, is chiral but crystallizes in a centrosymmetric space group as a racemate, the relative configuration at the stereogenic centres being 2S*,3R*,4S*. The cyclohexane ring adopts a half-chair conformation while the pyrazole ring has an envelope conformation. The crystal packing displays intermolecular O—H...N and N—H...O hydrogen bonding.

The methyl-amino-propyl chain in the title compound, C(13)H(21)NO, adopts an extended zigzag conformation and the N atom shows a trigonal coordination. The N atom acts as hydrogen-bond acceptor to the hy-droxy group of an adjacent mol-ecule, generating a helical chain running along the b axis. The amino H atom is not involved in hydrogen bonding.

The methyl-ene C atom in the title compound, C(13)H(16)N(2)S, is connected to a five-membered thia-zole ring and a mesityl substituent. The rings are aligned at 75.4 (1)°. The amino substitutent inter-acts with the ring N atom of an adjacent mol-ecule by an inter-molecular N-H⋯N hydrogen bond, generating a helical chain running along the b axis.

The C=C double-bond in the title compound, C13H13ClO3, has a Z configuration. The aliphatic substituents at one end of the double bond, i.e. the CH3CO– and C2H5O2C– groups, are aligned at 82.1 (3)° with respect to each other.

The title compound, C21H29NO6, is chiral with three stereogenic centres. The crystal is a racemate and consists of enantiomeric pairs with the relative configuration rac-(2R*,3S*,4R*). The ethyl fragment of the ethoxycarbonyl group at position 1 is disordered in a 0.60:0.40 ratio. The crystal packing displays intermolecular O—H...O hydrogen bonding. An intramolecular N—H...O hydrogen bond also occurs.

U-shaped calixsalens can be efficient building blocks for the construction of molecular boxes or cavitands. The first example of a calixsalen complex that has no coordination between the metal ion and phenolic oxygen atom was provided by X-ray. The resulting molecular structure has a high thermal stability, but completely degrades after the addition of DMSO.

Microwave irradiation of three component reaction of dimedone, appropriate aromatic aldehydes and amino alcohols in a stoichiometrical ratio 2:1:1 for few minutes afforded the formation of a stable fused three membered ring of the corresponding 3,6,6-tetramethyl-2,3,4,5,6,7,8,9,10-decahydroacridine-1,8-dione derivatives in an excellent yield (80–91%). The structure of all products has been characterized by X-ray crystal structural analyses, 13C NMR, 1H NMR, IR and mass spectrum analyses.

Radical reactions are involved in a multitude of relevant processes and their importance is increasingly recognized in different fields ranging from biochemistry to materials science. For instance, radical polymerization accounts for approximately 45% of world polymer production [1]; on the other hand, the involvement of transient radical species in enzyme regulated processes in living organisms has stimulated, in recent years, enormous research efforts to rationalize their role in key physiological processes like mitochondrial respiration and aging [2, 3] or in the pathogenesis of several diseases [4]. Perhaps the best known example of radical reaction is hydrocarbon autoxidation, a chain process that affects any organic material, from food to petrol‐derived chemicals to human beings, existing under an oxygen‐rich atmosphere [5]. As a consequence, antioxidants and radical‐chain inhibitors are among the most important compounds used to control key radical reactions [5]. They act by trapping chain‐carrying radical species, thereby competing with chain propagation, as illustrated in Scheme 20.1. Their rational design and use need to be strictly based on their reactivity with radical species. Indeed, the understanding of radical reactions and their role in biology, along with their use and control in synthetic chemistry or in medicine, requires detailed knowledge of their kinetics and how it is influenced by the reaction medium. In this chapter it will be explained how non‐covalent interactions control the rates and the products of reactions that are typical of the radicals involved in autoxidation, namely, peroxyl (ROO∙), phenoxyl (PhO∙), and alkoxyl (RO∙) radicals. These radicals are not only of biological interest, but they are also key intermediates in green synthesis protocols, which aim at obtaining fine chemicals from renewable materials under mild conditions. For this reason, we will illustrate some selected examples of biomimetic radical reactions that are made possible by the control of these reactive intermediates by non‐covalent interactions