Calix[5]arene (2) and calix[8]arene (4) reacted with bis(bromomethyl)‐substituted heterocycles such as pyridine and 1,10‐phenanthroline to give [1+1] condensation products 10 and 16–18 (bridged bimacrocycles) and [2+1] dicalixarenes 11, 13 and 14, all of which were fully characterized. Although the bridging capability of both bridging units 5 and 6 is surprisingly similar, calix[5]arene (2) could only be bridged with the pyridine derivatives 5. With calix[8]arene (4), the 1,10‐phenanthroline bridging reagent 6 gave a cleaner product spectrum than the pyridine reagent 5. The 1,10‐phenanthroline‐bridged calix[8]arene 16 was characterized by X‐ray analysis. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
The synthesis of the A,D-1,10-phenanthroline-bridged calix[6]arene 3 is improved by applying a new strategy for the synthesis of the important intermediate 2,9-bis(bromomethyl)-1,10-phenanthroline (2) and variation of the bridging conditions. Crystals were obtained from two different solvent systems. Two structures were determined by X-ray studies. Both analyses reveal a rare conformation for A,D-bridged ca-
A combination of experimental and quantum chemical results has been used to characterize dimethylfuroxan, (CH3)2C2N2O2, isolated in a matrix of solid Ar atoms at 12 K, and then to study its photoinduced isomerization and decomposition. The less-stable isomer 2,3-dinitrosobut-2-ene can be generated by UV photolysis (λmax = 254 nm). However, this species is photolabile and decomposes upon prolonged photolysis times with light having λmax = 254 nm or with IR radiation (λmax = 700 nm) to give CH3CNO as the final, photostable product. The two photoproducts were characterized using a combination of experimental and quantum chemical results. The work presented herein sheds light on the physical and chemical properties of furoxans, which may gain considerable importance as a source of NO, which itself plays a significant role as a biological messenger.
Several approaches to chiral derivatives of the 1,10-phenanthroline-bridged calix[6]arene 3 have been investigated, and seven new chiral calix [6]arenes have been synthesized. The C 2 -symmetric axially chiral bimacrocycle 5 has been synthesized as racemic mixture; calixarenes 8, 14, 18, 19, 20 and 21 carrying chiral substituents (camphorsulfonyl, myrtanyl) have been prepared using enantiomerically pure reagents.
The reaction of p-tert-butylcalix [6]arene with (+)-camphor-10-sulfonyl chloride gives either a mono-O-sulfonylated product or the fully O-sulfonylated calixarene. The crystal structure of mono-O-camphorsulfonylated p-tert-butylcalix [6]arene suggests that its sluggish reaction with further sulfonyl chloride can probably be explained by a conformation in which the narrow rim is covered by the camphor residue.Calixarenes are widely used building blocks for the construction of larger entities or even supramolecules. 2-6 A straightforward derivatization of calixarenes can obviously be carried out by transformation of one or more hydroxy groups into ethers or esters. Using reagents from the chiral pool, optical active products can be obtained. One such reagent is (+)-camphor-10-sulfonyl chloride which has already been reacted with three different calixarenes: with calix[4]-, 7 calix[5]-, 8 and calix[8]arene, 9 and different degrees of substitution have been observed.Remarkably, analogous calix[6]arenes have not yet been described, although calix[6]arene is readily available 10 and has been widely used.Therefore, (+)-camphor-10-sulfonyl chloride and calix[6]arene 1 were reacted in different ratios in the presence of triethylamine as a base. The use of one equivalent of the sulfonyl chloride gave the monosubstituted chiral derivative 2 in 54% yield. Next, the sulfonyl chloride was used in excess but even when three equivalents were used, the only isolated product was the monosubstituted calixarene 2.When the amount of the sulfonyl chloride was increased drastically, oligosulfonylated products were formed but none of them in a useful quantity (in addition to the formation of di-, tri-, tetra-, penta-, and hexasubstituted derivatives, also the formation of regioisomers must be considered for di-, tri-, and tetrasubstituted products).Only the use of a large excess of (+)-camphor-10-sulfonyl chloride led to a synthetically useful amount of product containing more than one camphor unit. The hexasulfonylated calix[6]arene 3 was thus obtained in 74% yield.The fact that only the single and fully substituted products 2 and 3 were formed in good yields is a surprise. It seems that the second substitution is hindered. Three equivalents of sulfonyl chloride still predominantly yield the monosubstituted product 2. But once a certain excess of sulfonyl chloride is used, more than one or two hydroxy groups do react, and a complex mixture of oligosubstituted products is found. An X-ray structure of the monosubstituted calix[6]arene 2 sheds light onto this puzzle. In the crystal, the camphorsulfonyl residue covers the narrow rim of the calixarene, thus probably obstructing further sulfonylation (see Figure 2). Although the structure in solution is more flexible, this obstruction may be the cause for the sluggish sulfonylation of a second phenol in 2. However, if eventually a second sulfonyl group is introduced, the two substituents will repulse one another and they will occupy positions different from that found in the crystal of 2. Th...
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