Diethynyl paracyclophane

There are several stereoisomers in disubstituted [2.2]paracyclophane, such as ortho-, meta-, para-, pstudo-ortho-, pseudo-m fa-, pseudo-para-, and pseudo-g mma/-disubstituted [2.2]paracyclophanes. Iron-catalyzed dibromination of commercially available [2.2]paracyclophane yields the mixtures of the dibromo[2.2]paracyclo-phane isomers, and pseudo-para-dibromo[2.2]paracyclophane 9 can be obtained by recrystallization as it has the poorest solubility in common organic solvents [76]. Thermal isomerization of 9 in triglyme afforded the psowdo-ortho isomer 38, as shown in Scheme 10. This transformation is an equilibrium reaction when the reaction was allowed to cool to room temperature, pseudo-para isomer 9 was precipitated as a result of its low solubility and was readily separated by simple filtration to obtain pseudo-arf/za isomer 38 in moderate isolated yield [76]. V ondo-ortho-dibromo[2.2]paracyclophane 38 was converted into pseudo-arf/ a-diethynyl[2.2] paracyclophane 40 via pseudo-arf/ a-diformyl[2.2]paracyclophane 39 (Scheme 10) [77]. Sonogashira-Hagihara coupling polymerization of 40 with 12 afforded the corresponding jc-stacked polymer 41 in 23 % isolated yield with the of 3,800 [78]. 

This intermediate was allowed to react with electrophiles such as DMF to obtain (/ p)-pseudo-6>r /i6>-diformyl[2.2]paracyclophane (/ p)-39 in 71 % isolated yield (Scheme 11). Enantiomer (Sp)-39 was obtained in 87 % isolated yield from (Sp,S)-2 through the same route. The formyl groups of (/ p)-39 were converted into the ethy-nyl groups using the Ohira-Bestmann reagent to give enantiopure (/ p)-pseudo-(9rr/i6>-diethynyl[2.2]paracyclophane (/ p)-40 in 60 % isolated yield the enantiomer (5p)-40 was similarly obtained in 57 % yield. 

A Wittig reaction of the diformyl[2.2]paracyclophane with methyltriphenyl-phosphonium bromide affords the corresponding divinyl[2.2]paracyclophane (Fig. 16c) [92,93]. Treatment of the dialdehyde with the Bestmann-Ohira reagent (CH3C0CN2P0(0CH3)2) provides the corresponding diethynyl[2.2]paracyclophane [94-96]. 

Fig. 15 Preparation of ethynyl and vinyl [2.2]paracyclophanes (a) Divinyl and diethynyl compounds from dibromo[2.2]paracyclophanes (b) cross and step tetra(ethyne)s prepared...

Fig. 16 Preparation and reactions of diformyl[2.2]paracyclophanes. (a) formylation of dibromo [2.2]paracyclophanes (b) preparation of pseudogeminal diformyl[2.2]paracyclophane (c) Wittig and Bestmann-Ohira reactions of aldehydes to afford divinyl and diethynyl compounds, respectively (d) preparation of 4,5,12,13-substituted [2.2]paracyclophanes by Diels-Alder reaction between 1,2,4,5-hexatetrene and substituted alkynes (e) preparation of step tetrasubstituted compounds from 1,2-disubstituted ethynes...

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