Copper-Catalyzed Carbonylative Cross-Coupling of Alkyl Iodides and Amines.

A general copper-catalyzed carbonylative cross-coupling between amines and alkyl iodides is reported. Using a simple combination of catalytic amounts of copper(I) chloride and N,N,N',N",N"-pentamethyldiethylenetriamine in the presence of sodium hydroxide under carbon monoxide pressure, a broad range of alkyl iodides and amines can be efficiently coupled to the corresponding amides that are obtained in good to excellent yields. Notable features of this process - the first one relying on a base metal catalyst - include the availability and low cost of the catalytic system, its successful use with primary, secondary, tertiary alkyl iodides and all classes of amines - with no or limited competing nucleophilic substitution without CO incorporation - as well as its efficiency with complex alkyl iodides and amines. Mechanistic studies demonstrated that a radical pathway is operative and the key role of CO.

Amine-Directed Palladium-Catalyzed C-H Halogenation of Phenylalanine Derivatives.

Invited for the cover of this issue are Jean-François Brière, Cédric Schneider, Guillaume Journot and co-workers from the COBRA laboratory and Oril Industrie (Normandy, France). The image shows the progression from questioning how to easily and regioselectively introduce halogen atoms to amino acids to the discovery of a catalytic functional-group-directed C-H halogenation of phenylalanine derivatives. Read the full text of the article at 10.1002/chem.202102411.

Amine-Directed Palladium-Catalyzed C-H Halogenation of Phenylalanine Derivatives.

An efficient primary-amine-directed, palladium-catalyzed C-H halogenation (X=I, Br, Cl) of phenylalanine derivatives is reported on a range of quaternary amino acid (AA) derivatives thanks to suitable conditions employing trifluoroacetic acid as additive. The extension of this original native functionality-directed ortho-selective halogenation was even demonstrated with the more challenging native phenylalanine as tertiary AA.

Biomimetic total synthesis of santalin†Y.

A biomimetic total synthesis of santalin Y, a structurally complex but racemic natural product, is described. The key step is proposed to be a (3+2) cycloaddition of a benzylstyrene to a "vinylogous oxidopyrylium", which is followed by an intramolecular Friedel-Crafts reaction. This cascade generates the unique oxafenestrane framework of the target molecule and sets its five stereocenters in one operation. Our work provides rapid access to santalin Y and clarifies its biosynthetic relationship with other colorants isolated from red sandalwood.

Improving physical properties via C-H oxidation: chemical and enzymatic approaches.

Physicochemical properties constitute a key factor for the success of a drug candidate. Whereas many strategies to improve the physicochemical properties of small heterocycle-type leads exist, complex hydrocarbon skeletons are more challenging to derivatize because of the absence of functional groups. A variety of C-H oxidation methods have been explored on the betulin skeleton to improve the solubility of this very bioactive, yet poorly water-soluble, natural product. Capitalizing on the innate reactivity of the molecule, as well as the few molecular handles present on the core, allowed oxidations at different positions across the pentacyclic structure. Enzymatic oxidations afforded several orthogonal oxidations to chemical methods. Solubility measurements showed an enhancement for many of the synthesized compounds.

Phase-transformation-induced twinning of an iron(III) calix[4]pyrrolidine complex.

The title compound, tetrachlorido-1κCl;2κ(3)Cl-(2,2,7,7,12,12,17,17-octamethyl-21,22,23,24-tetraazapentacyclo[16.2.1.1(3,6).1(8,11).1(13,16)]tetracosane-1κ(4)N,N',N'',N''')-µ2-oxido-diiron(III), [Fe2Cl4O(C28H52N4)], undergoes a slow phase transformation at ca 173 K from monoclinic space group P2(1)/n, denoted form (I), to the maximal non-isomorphic subgroup, triclinic space group P1, denoted form (II), which is accompanied by nonmerohedral twinning [twin fractions of 0.693 (4) and 0.307 (4)]. The transformation was found to be reversible, as on raising the temperature the crystal reverted to monoclinic form (I). In the asymmetric unit of form (I), Z' = 1, while in form (II), Z' = 2, with a very small reduction (ca 1.8%) in the unit-cell volume. The two independent molecules (A and B) in form (II) are related by a pseudo-twofold screw axis along the b axis. The molecular overlay of molecule A on molecule B has an r.m.s. deviation of 0.353 Å, with the largest distance between two equivalent atoms being 1.202 Å. The reaction of calix[4]pyrrolidine, the fully reduced form of meso-octamethylporphyrinogen, with FeCl3 gave a red-brown solid that was recrystallized from ethanol in air, resulting in the formation of the title compound. In both forms, (I) and (II), the Fe(III) atoms are coordinated to the macrocyclic ligand and have distorted octahedral FeN4OCl coordination spheres. These Fe(III) atoms lie out of the mean plane of the four N atoms, displaced towards the O atom of the [OFeCl3] unit by 0.2265 (5) Šin form (I), and by 0.2210 (14) and 0.2089 (14) Å, respectively, in the two independent molecules (A and B) of form (II). The geometry of the [OFeCl3] units are similar, with each Fe(III) atom having a tetrahedral coordination sphere. The NH H atoms are directed below the planes of the macrocycles and are hydrogen bonded to the coordinated Cl(-) ions. There are also intramolecular C-H···Cl hydrogen bonds present in both (I) and (II). In form (I), there are no significant intermolecular interactions present. In form (II), the individual molecules are arranged in alternate layers parallel to the ac plane. The B molecules are linked by a C-H···Cl hydrogen bond, forming chains along [100].

4-Meth-oxy-benzoyl-meso-octa-methyl-calix[2]pyrrolidino[2]pyrrole: an acyl chloride derivative of a partially reduced calix[4]pyrrole.

In the title compound, C(36)H(50)N(4)O(2), the two pyrrolidine rings have envelope conformations. The conformation of the macrocycle is stabilized by N-H⋯N hydrogen bonds and a C-H⋯N inter-action. The benzoyl ring is inclined to an adjacent pyrrole ring by 6.76 (9)°, with a centroid-to-centroid distance of 3.6285 (10) Å. In the crystal, apart from a C-H⋯O and a C-H⋯π inter-action, mol-ecules are linked via an N-H⋯O hydrogen bond, leading to the formation of helical chains propagating along [010].

4-Chloro-benzoyl-meso-octa-methyl-calix[2]pyrrolidino[2]pyrrole: an acyl chloride derivative of a partially reduced calix[4] pyrrole.

In the title compound, C(35)H(47)ClN(4)O, the two pyrrolidine rings have envelope conformations. The conformation of the macrocycle is stabilized by N-H⋯N hydrogen bonds and a C-H⋯N inter-action. The benzoyl ring is inclined to the adjacent pyrrole ring by 11.66 (11)°, with a centroid-centroid distance of 3.7488 (13) Å. In the crystal, molecules are linked by N-H⋯O hydrogen bonds into helical chains propagating in [010] and C-H⋯O and C-H⋯π interactions are also observed.

2,2'-[(2S*,6R*)-Piperidine-2,6-di-yl]-di-pro-pan-2-ol.

In the title compound, C(11)H(23)NO(2), the piperidine ring has a chair conformation. The two hy-droxy H atoms are disordered over two positions with fixed occupancy ratios of 0.57:0.43 and 0.63:0.37. In the mol-ecule, there are two short N-H⋯O inter-actions. In the crystal, four symmetry-related mol-ecules are linked by O-H⋯O hydrogen bonds to form a cage-like arrangement, centered about the point of inter-section of three twofold axes. These cages stack along the [100] direction.

2-[2-(pyrrolidin-2-yl)propan-2-yl]-1H-pyrrole and its amide derivative 1-{2-[2-(1H-pyrrol-2-yl)propan-2-yl]pyrrolidin-1-yl}ethanone.

In the title compounds, C(11)H(18)N(2), (II), and C(13)H(20)N(2)O, (III), the pyrrolidine rings have twist conformations. Compound (II) crystallizes with two independent molecules (A and B) in the asymmetric unit. The mean planes of the pyrrole and pyrrolidine rings are inclined to one another by 89.99 (11) and 89.35 (10)° in molecules A and B, respectively. In (III), the amide derivative of (II), the same dihedral angle is much smaller, at only 13.42 (10)°. In the crystal structure of (II), the individual molecules are linked via N-H...N hydrogen bonds to form inversion dimers, each with an R(2)(2)(12) graph-set motif. In the crystal structure of (III), the molecules are linked via N-H...O hydrogen bonds to form inversion dimers with an R(2)(2)(16) graph-set motif.

Catalytic hydrogenation of meso-octamethylporphyrinogen (calix[4]pyrrole).

Hydrogenation of meso-octamethylporphyrinogen (calix[4]pyrrole) with a number of heterogeneous catalysts under different experimental conditions has been investigated. GC-MS analyses of the reaction mixtures showed the formation of one to four products in low to moderate yields: three of them were diastereoisomers of the product derived from half-hydrogenation of the substrate, and displayed alternating pyrrolidine and pyrrole rings, while the fourth was the all-cis saturated product. An acidic medium was necessary to achieve hydrogenation. However, the use of too strongly acidic solvents or additives was detrimental to the stability of the substrate and/or the catalyst.

2,2'-(Propane-2,2-di-yl)bis-(1H-pyrrole).

The title compound, C(11)H(14)N(2), crystallized with two independent mol-ecules (A and B) in the asymmetric unit. The two mol-ecules differ only slightly, with the pyrrole rings being inclined to one another at a dihedral angle of 87.67 (8)° in mol-ecule A and 88.09 (7)° in mol-ecule B. In the crystal, there are no classical hydrogen bonds, but the two pyrrole NH groups of one mol-ecule are involved in N-H⋯π inter-actions with the pyrrole rings of the other mol-ecule. In this manner, a compact box-like arrangement of the two independent mol-ecules is formed.

4,4-Bis(1H-pyrrol-2-yl)penta-nol.

The title achiral compound, C(13)H(18)N(2)O, crystallized in the chiral monoclinic space group P2(1). The pyrrole rings are inclined to one another by 62.30 (11)°, and the propanol chain is in an extended conformation. In the crystal, the two pyrrole NH groups are involved in inter-molecular N-H⋯O hydrogen bonds, leading to the formation of a helical arrangement propagating along the b axis. An inter-esting feature of the crystal structure is the absence of any conventional hydrogen bonds involving the hydr-oxy H atom. There is, however, a weak inter-molecular O-H⋯π inter-action involving one of the pyrrole rings.