The Elusive beta-unsubstituted calix[5]pyrrole finally captured

[reaction: see text] The meso-decamethyl-calix[5]pyrrole 2b was synthesized from the furan-based analogue 1b via the homologation of the furan rings to pyrrole, and its solid-state structure was determined by X-ray crystallography: surprisingly, the binding constant of 2b toward chloride is found to be lower than that of the tetrameric analogue 2a.     

pH‐Controlled Molecular Switches and the Substrate‐Directed Self‐Assembly of Molecular Capsules with a Calix[4]pyrrole Derivative

10α,20α‐Bis(4‐nitrophenyl)calix[4]pyrrole ( 1 ) forms 1:1 complexes with anions of selected aromatic hydroxy acids in which the host orientation within the guest is controlled by a change in the pH value. Some bis‐anionic guests, including those obtained from 4‐hydroxybenzoic acid, 1,4‐ and 1,3‐benzenedicarboxylic acids, induce the self‐assembly of molecular capsules involving two molecules of the receptor. ¹H NMR data and solid‐state structures of the 1:1 complex of 1 with p‐C₆H₄(COOH)(COO^?)⁺NMe₄ and the 2:1 capsule [( 1 )₂m‐C₆H₄(COO^?)₂(⁺NMe₄)₂] provide structural details in solution and in the solid state.     

Efficient organocatalysis with a calix[4]pyrrole derivative

The 10α,20β-bis(4-nitrophenyl)-calix[4]pyrrole was found to act as an effective organocatalyst for the hetero Diels-Alder reaction of Danishefsky’s diene with aromatic aldehydes. This discovery is the first reported case of a calixpyrrole that exhibits organocatalytic activity.     

Regioselective O-alkylations and acylations of polyphenolic substrates using a calix[4]pyrrole derivative

The 10α,20α-bis(4-nitrophenyl)-calix[4]pyrrole 2 can act as a topologically selective protecting group in the O-alkylation and acylation of polyphenolic polycyclic aromatic compounds thanks to the regioselective formation of phenolate-type complexes. Remarkably, the host-guest interaction with the anionic reagents is sufficiently strong and kinetically slow to produce a high degree of selectivity.     

Host–Guest Chemistry of a Bis‐Calix[4]pyrrole Derivative Containing a trans/cis‐Switchable Azobenzene Unit with Several Aliphatic Bis‐Carboxylates

The azobenzene unit used as a photochemically and thermally switchable linker in the assembly of a bis‐calix[4]pyrrole receptor provides a means to modulate the binding of bis‐carboxylates of significant biological importance in cancer research. Conversely, the complexation of different bis‐anionic guests has significant kinetic effects on both the photochemical and thermal trans/cis isomerization of the azobenzene unit.     

From calixfurans to heterocyclophanes containing isopyrazole units

Cyclic poly-1,4-diketones 2, obtained by the oxidation of the furan units present in calix[4]furan 1a and calix[6]furan 1c have been converted into the novel heterocyclophanes 4a and 4c containing four and six isopyrazole units, respectively. Solution studies have demonstrated the ability of 4a and 4c to act as ligands for transition metals. The crystal structures of 4a and the coordination compound formed by 4c with 2 equiv. of cis-PtCl₂(DMSO)₂ have been determined. In the solid state 4c is shown to bind aromatic substrates within its cavity.     

Syntheses, structures, and anion-binding properties of two novel calix[2]benzo[4]pyrroles

Calix[2]benzo[4]pyrrole m-6 and p-6, each containing two dipyrromethane moieties and two m-phenylene or p-phenylene units, respectively, were readily synthesised from pyrrole, 1,3- and 1,4-bis(1,1'-dimethylhydroxymethyl)benzene, (m-4 and p-4, respectively) and acetone. Macrocycles m-6 and p-6 were tested as receptors for a selection of anions, such as acetate, dihydrogenphosphate and fluoride. The X-ray structures of m-6 and p-6 and those of the complexes m-6F(-), m-6Cl(-) and m-6CH(3)COO(-) (with an nBu(4)N(+) counterion) were also determined.     

THE USE OF STATISTICAL TOOLS TO CONTEND WITH VARIABILITY IN ENGINEERING

In summary, the statistical series of Experimental Techniques will cover a wide range of topics and methodologies. The intent of the series is to widen the engineer's use of statistical techniques through a number of articles based on theory, examples, and case studies. Topics to be covered will include statistically designed experiments, variance components, control charting, distribution tests, bootstrap methods, and probabilistic design. Other topics such as graphical techniques for exploratory data purposes, statistical intervals, and discriminate analysis through the use of frequency domain data may also be covered as well. Hopefully, the articles will prove to be informative and provide enough detail for the engineer to go beyond the calculation of a mean and a standard deviation in their daily analysis of data. A listing of future articles follows.