Belts, molecular

Another fascinating all-carbon molecule, the molecular belt 21a, is an isomer of Cm and can be constructed from six non-planar TEE subunits (Figure 10).1491 Semiempirical calculations (AMI) indicate... 

Figure 10. Molecular belt 21a, an isomer of buck-minsterfullerene C6o, and its hypothetical [2+2] polymer 21b...

Volume 75 concludes with six procedures for the preparation of valuable building blocks. The first, 6,7-DIHYDROCYCLOPENTA-l,3-DIOXIN-5(4H)-ONE, serves as an effective /3-keto vinyl cation equivalent when subjected to reductive and alkylative 1,3-carbonyl transpositions. 3-CYCLOPENTENE-l-CARBOXYLIC ACID, the second procedure in this series, is prepared via the reaction of dimethyl malonate and cis-l,4-dichloro-2-butene, followed by hydrolysis and decarboxylation. The use of tetrahaloarenes as diaryne equivalents for the potential construction of molecular belts, collars, and strips is demonstrated with the preparation of anti- and syn-l,4,5,8-TETRAHYDROANTHRACENE 1,4 5,8-DIEPOXIDES. Also of potential interest to the organic materials community is 8,8-DICYANOHEPTAFULVENE, prepared by the condensation of cycloheptatrienylium tetrafluoroborate with bromomalononitrile. The preparation of 2-PHENYL-l-PYRROLINE, an important heterocycle for the synthesis of a variety of alkaloids and pyrroloisoquinoline antidepressants, illustrates the utility of the inexpensive N-vinylpyrrolidin-2-one as an effective 3-aminopropyl carbanion equivalent. The final preparation in Volume 75, cis-4a(S), 8a(R)-PERHYDRO-6(2H)-ISOQUINOLINONES, il lustrates the conversion of quinine via oxidative degradation to meroquinene esters that are subsequently cyclized to N-acylated cis-perhydroisoquinolones and as such represent attractive building blocks now readily available in the pool of chiral substrates. 

They have served as starting points for the synthesis of molecular belts, collars, and strips.16... 

Molecular belts, molecular knots and trefoil knots, propellanes and pagodanes, even such a unique molecule like footballene or buckminsterfullerene belong to these compounds which remind the observer of a comparable macroscopic object [ ] ... 

In 1983, Vogtle [5] proposed the synthesis of 1, a molecular belt with a completely aromatic carbon skeleton. The benzenoid nuclei are fused laterally in a polyacene-like manner. The compound which could be called superacene [5] is a representative of the [njcyclacenes 2 which gained more and more interest in the following years. 

Another class of rr-spherands with a belt-shaped structure originates from the connection of 1,4-cyclohexanediylidene units to macrocycles of type 24. However, in contrast to the beltenes the rr-bonds are in the plane of the ring and not perpendicular to it. The most simple representative of this class (n = 2) is tricyclo[4.2.2.2 ]dodeca-l,5-diene (25) synthesized in 1981 by Wiberg et al. [23], but due to its small size it cannot be called a molecular belt. 

R167 M. lyoda, Y. Kuwatani, T. Nishinaga, M. Takase and T. Nishiuchi, Conjugated Molecular Belts Based on 3D Benzaannulene Systems , in Fragments of Fullerenes and Carbon Nanotubes Designed Synthesis, Unusual Reactions, and Coordination Chemistry, eds. M. A. Petrukhina and L. T. Scott, John Wiley Sons, Inc., Hoboken, N. J., 2012, p. 311. 

Shinkai, S - Molecular recognition of calixarene-based host molecules 193 Stephenson, N. A. - see Busch, D. H. 137 Stoddart, J. F. - The making of molecular belts and collars 227 Sutherland, I O. - Molecular recognition by macropolycycUc hosts 213... 

Keywords Cyclacene Cycloparaphenylene Cyclophenacene Molecular belt Picotube... 

Fig. 3 Representative molecular belts (clockwise from top left, cyclocarbon, cyclophenacene, picotube, cyclacene, cycloparaphenylene, and cycloparaphenyleneacetylene)...

Having overcome the challenge of [6]CPPA and [8]CPPA with his landmark synthesis, Kawase improved upon these methods to prepare large quantities of [6]-[9] CPPA. With ample material in hand, the Kawase lab sought to exploit the unique, electron-rich cavity present in these rigid molecular belts [16]. Kawase showed for the first time that CPPAs can form all-hydrocarbon inclusion complexes with appropriate guests [17]. By co-crystallizing [6]CPPA and [8]CPPA with hexamethylbenzene and toluene respectively, crystal stmctures of a 1 1 12 HMB and 1 4 13 tol complexes were obtained (Pig. 9). 

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