Hexa cyclophane

The penultimate example of macrocycles based on phenyl and acetylenic units has been the very recent report by Tobe [801 and Rubin [81] of cyclophane 134. Both groups generated 134 in the mass spectrometer by laser desorption of hexa-protected polyynes 135 (robust) and 136 (unstable), respectively (Scheme 31). 

The observed tt-IP s were compared with calculated values, obtained from four 7t-electron models. On the whole the agreement between calculated and observed k-IP s was good, indicating that transannular effects are not present. The authors ascribe the absence of such an effect in helicenes to the greater flexibility of these molecules, compared with cyclophanes. From and INDO-MO-calculation on hexa-helicene 121) it was concluded that the four HOMO S have predominantly Jt-character, in contrast to the other occupied MO s. A linear combination of the four MO S... 

Monolayered cyclophane complexes of type 263 are also reduced by sodium bis(methoxyethoxy)aluminum hydride (Red-Al) to give (i74-diene)-(i76-cyclophane)ruthenium(0) complexes (Scheme 33). If the benzene ring of 263 (arene = benzene) is converted to the (1,3-cyclohexadiene)-ruthenium(O) derivative 271, however, when the corresponding rj6-hexa-methylbenzene is reduced with Red-Al, the product is the (if-1, 4-cyclohexadiene)ruthenium(0) complex 288. Synthesis of 271 can... 

Examples in this series, whose cyclohexadiene units are all formally related by oxidation to meta (types V, VI and IX) and para (types VII and VIII) bridged cyclophanes of the kinds (192) and (193), respectively, appear not to exist in the literature (or they are at least rare and have escaped the attention of the authors of this review). Cyclophanes appear in standard textbooks and there is a recent example of a 2,5-bridged hexa-l,3,S-triene, namely (194), °° related by electrocyclization to a type VII 1,4-bridged cyclohexadiene. It is interesting that (194) is representative of a doubly orthogonal conformer of hexa-1,3,5-triene. However, the electrocyclization of hexatrienes to bridged 1,3-cyclohexadienes appears not to have been previously investigated. 

Cram and co-workers described complexation of [2.2]paracyclophane or para-phenylene unit containing crown compounds with primary ammonium salts, diammonium salts and alkali metal salts [23, 24]. Compound 5 makes complexes with tert-butylammonium thiocyanate (1 2 stoichiometry) and hexa-methylenediammonium or decamethylenediammonium hexafluorophosphate (1 1 stoichiometry). Cyclophanes 5-7 (Structure 2) solubilized 2 molar equivalent of tert-butylammonium tetraphenylborate in CHCI3 due to the resulting lipophilic complexes. 

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