Information AboutCyclophane |
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strain]]. Despite this, cyclophane structures are not unknown to biomolecules. Basic cyclophane types are ('''I''') in ''scheme 1'', '''[n paracyclophanes''' ('''II''') and '''[n,n']cyclophanes''' ('''III'''). the prefixes ''meta'' and ''para'' correspond to the usual Arene Substitution Patterns and n refers to the number of atoms making up the bridge. STRUCTURE Paracyclophanes adopt the , 119, 2698 (1986). In organic reactions {Link without Title} cyclophane tends to react as a diene derivative and not as an aromat. With Bromine it gives 1,4-addition and with Chlorine the 1,2-addition product forms. Yet the Proton NMR spectrum displays the aromatic protons and their usual deshielded positions around 7.2 ppm and the central methylene protons in the aliphatic bridge are even severely deshielded to a position of around - 0.5 ppm, that is, even deshielded compared to the internal reference Tetramethylsilane . With respect to the Diamagnetic Ring Current criterion for aromaticity this cyclophane is still aromatic. One particular research field in cyclophanes involves probing just how close atoms can get above the center of an aromatic nucleus ''Molecular Iron Maidens: Ultrashort Nonbonded Contacts in Cyclophanes and Other Crowded Molecules'' Robert A. Pascal, Jr Eur. J. Org. Chem. 2004, 3763-3771 . In so-called in-cyclophanes with part of the molecule forced to point '''in'''wards one of the closest hydrogen to arene distances experimentally determined is just 168 Picometer . A non-bonding nitrogen to arene distance of 244 pm is recorded for a pyridinophane and in the totally weird Superphane the two benzene rings are separated by a mere 262 pm. Another representative of this group are In-methylcyclophane s. SYNTHETIC METHODS can be synthesized ''[6 Paracyclophane'' Vinayak V. Kane, Anthony D. Wolf, Maitland Jones, , Jr. with Spiro Ketone 1 in ''scheme 3'' rearranging in a Pyrolysis reaction through the Carbene intermediate '''4'''. The cyclophane can be Photochemically converted to the Dewar Benzene '''6''' and back again by application of heat. A separate route to the Dewar form is by a cationic Silver Perchlorate induced Rearrangement Reaction of the bicyclopropenyl copound '''7'''. Metaparacyclophanes constitute another class of cyclophans like the ''[14 First Example of an [m [n]Metaparacyclophane''Chunmei Wei, Kai-For Mo, and Tze-Lock Chan of Dibromide by Disulfide . Then Oxidation of sulfide to Sulfone by Hydrogen Peroxide followed by in-situ Ramberg-Bäcklund Reaction with halide donor dibromodifluoromethane and base Potassium Hydroxide . Final step Hydrogenation pf Alkene by hydrogen and Palladium On Carbon featuring a in-situ Ramberg-Bäcklund Reaction converting the Sulfone '''3''' to the Alkene '''4'''. NATURALLY OCCURRING CYCLOPHANES Despite carrying strain, the cyclophane motif does exist in nature. One example of a metacyclophane is Cavicularin . Haouamine A is a paracyclophane found in a certain species of Tunicate . Because of its potential application as an anticancer Drug it is also available from Total Synthesis via an Alkyne - Pyrone Diels-Alder Reaction in the crucial step with expulsion of carbon dioxide (''scheme 5'') ''Total Synthesis of (±)-Haouamine A'' Phil S. Baran and Noah Z. Burns J. Am. Chem. Soc. ; 2006; ASAP Web Release Date: 04-Mar-2006; Abstract The authors mark the biosynthetic origin as ''mysterious''. In this compound the deviation from planarity is 13° for the benzene ring and 17° for the bridgehead carbons ''Synthesis of the 3-Aza- Core of Haouamine A and B'' Peter Wipf and Markus Furegati Org. Lett.; 2006; 8(9) pp 1901 - 1904; (Letter) [http://dx.doi.org/10.1021/ol060455e Abstract . An alternative cyclophane formation strategy in ''scheme 6'' Scheme 6. Reaction scheme: step I Elimination Reaction of methanol with Trifluoroethanol and Diisopropylamine , step II Methylation with Dimethylsulfate . Ns = Nosylate was developed based on Aromatization of the ring well after the formation of the bridge. {LINK WITHOUT TITLE} PARACYCLOPHANES A well exploited member of the family is [2,2 cyclophane. One method for its preparation is by a 1,6-Hofmann Elimination Organic Syntheses , Coll. Vol. 5, p.883 ('''1973'''); Vol. 42, p.83 ('''1962''') Link .: The {Link without Title} paracyclophane-1,9-diene has been applied in ROMP to a Poly(p-phenylene Vinylene) with alternating Cis-alkene and Trans-alkene bonds using Grubb's Second Generation Catalyst ''Soluble Poly(p-phenylenevinylene)s through Ring-Opening Metathesis Polymerization'' Chin-Yang Yu and Michael L. Turner Angew. Chem. Int. Ed. 2006, 45, 7797 –7800 : The driving force for ring-opening and polymerization is strain relief. The reaction is believed to be a Living Polymerization due to the lack of competing reactions. Because the two benzene rings are in close proximity this cyclophane type also serves as guinea pig for ; 2006; 128(51) pp 16508 - 16509; (Communication) : The product formed has an between the aromatic Pi Electron s and the Sigma Electrons in the C-N bond in the reactants LUMO . REFERENCES |
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