-90°C). When the temperature was near -60°C. quenching of the solution in water and standard workup afforded crude reaction products in ca. 90Yo yield (GC). Purification (recrystallization or column chromatography) gave pure products.[9] Only the Markownikoff regioisomer 9 (by GC and I3C NMR analyses) was fund to be present in yields of 69%-91% after quenching in water.Academic Press, Orlando, FL, USA 1984, Chapter 5, p. 341. Chem. 88 (1976 Cyclobis(paraquat-p-phenylene). A Tetracationic Multipurpose ReceptorBy Barbara Odell, Mark V. Reddington, Alexandra M. Z . Slawin, Neil Spencer, J. Fraser Stoddart,* and David J . WilliamsRecently, we reported''] on cyclophane-like molecular receptors, such as bisparaphenylene-34-crown-10 1, which contains n-electron-rich hydroquinone units for face-to-face complexation ( Fig. 1) with paraquat 2, a n-electron-deficient dication. These observations led us to propose that it might be possible to reverse constitutionally the roles of the receptor and the substrate and so bind a n-electronrich diphenol ether, such as 1,4-dimethoxybenzene 3a, inside a tetracationic molecular receptor (Fig. 1). Such a receptor is the tetracation cyclobis(paraquat-p-phenylene) 4 which incorporates two n-electron-deficient paraquat residues connected in a phane-like manner by means of two para-phenylene groups.[21 Here, we describe (i) the synthesis of 4 as its tetrakis(hexafluorophosphate) 4 . 4 PF,, (ii) its X-ray structural characterization as the acetonitrile solvate 4 . 4 PF6.3 MeCN, (iii) the UV and 'H-NMR spectroscopic evidence for 1 : 1 complex formation (a) between 4 . 4 PF6 and 1,2-, 1,3-, and 1,4-dimethoxybenzene 3a/3b/ 3c in acetonitrile (CD,CN) and (b) between 4 . 4 C I and 1,4-dihydroxybenzene 6 in water (D20)J3' and (iv) the results of molecular and semiempirical quantum mechanical calculations on 4 and on 4 . 2 MeCN.[ Fig. 1 Schematic representation of the basis for the proposal that the cyclobis(paraquat-p-phenylene) 4 should act as a tetracationic receptor for 1,4-dimethoxybenzene 3a.The procedure (cf. Ref.[2]) employed for the preparation of 4 -4 P F 6 starting from the bis(pyridinium) salt 5 and 1,4-bis(bromomethyl)benzene is outlined in Scheme 1. (Fig. 2, top) that 4 adopts a rigid centrosymmetric rectangular box-like conformation with the two paraquat units forming the longer sides and the two para-xylylene residues, the shorter ones. There is a 19" twist angle between the two pyridinium rings of each paraquat unit: in addition, there are deformations of both the paraquat and para-xylylene components producing a bowing of the sides of the cyclophane. Thus, the strain within the molecule is relieved by out-of-plane bending of the six aromatic rings and is distributed throughout the macrocycle with the maximum deviations associated with the exocyclic C-CH2 bonds emanating from the para-phenylene residues: these bonds subtend an angle of 14" with respect to each other whilst the two Ne-CH, bonds associated with the paraquat units subtend an angle of 23 O . There is also a con...

Hexafluoroisopropan-2-ol (HFIP) has been found to be an unusually beneficial solvent for undertaking hypervalent iodine-initiated [2+2] cycloaddition of styrenes. For the initiator phenyliodine(III) diacetate (PIDA), voltammetric data demonstrate that the enhanced reactivity in HFIP is due to its greater oxidizing abilities in this fluorinated solvent such that in HFIP the reactivity of PIDA is comparable if not superior to its fluorinated analog phenyliodine(III) bis(trifluoroacetate). These results contrast with the often reported view that the role of the fluoroalcohol is to stabilize a radical cation formed by single electron transfer. Moreover, combined NMR and HRMS results reveal the formation of a strong H-bonded adduct between the solvent and oxidizing reagent which is the physical origin of the observed altered synthetic reactivity.

Round the bend: Bending a molecular wire round an eight‐spoked template leads to the formation of a highly symmetric belt‐shaped π system (green in picture). Addition of a large excess of pyridine releases the corresponding cyclic octamer from the template.

Electronic communication between concentric macrocycles with wave functions that extend around their circumferences can lead to remarkable behavior, as illustrated by multiwalled carbon nanotubes and photosynthetic chlorophyll arrays. However, it is difficult to hold one π-conjugated molecular ring inside another. Here, we show that ring-in-ring complexes, consisting of a 6-porphyrin ring locked inside a 12-porphyrin ring, can be assembled by placing different metals in the two rings (zinc and aluminum). A bridging ligand with carboxylate and imidazole binding sites forms spokes between the two rings, resulting in a highly cooperative supramolecular self-assembly process. Excitation is transferred from the inner 6-ring to the outer 12-ring of this Russian doll complex within 40 ps. These complexes lead to a form of template-directed synthesis in which one nanoring promotes formation of a larger concentric homologous ring; here, the effective template is an eight-component noncovalent assembly. Russian doll templating provides a new approach to amplifying the size of a covalent nanostructure.