Layered Paracyclophanes Chochins

Ingenious approaches have been developed for the syntheses of multi-layered [2.2]-paracyclophanes and especially for optically active representatives with known chiralities. For such gyrochiral structures with C2- or Z 2-symmetry the genetic name [n]chochins was proposed (meaning an oldfashioned Japanese lantern)64) where n represents the number of layers. Parts of their chemistry have been reviewed17). 

For the syntheses of such chochins both the 1,6-Hofmann elimination reactions of suitable [2.2]paracyclophane derivatives with p-xylyl ammoniumbases (e.g. 36 and 37 — as used for the first synthesis of a [4]chochin 43 65) — and the photodesulfurization method l7,66) have proved applicable. 

5 Chirality — especially together with the description (R) or (5) — will be used in this survey in the sense of absolute chirality and absolute configuration , respectively (see ilso Ref.211 and Sect. 2.9.). 

6 The authors441 remarked that the optical instability of [lOJparacyclophaneearboxylic acid (14) had caused them to use the methyl derivative 15 instead, although it had been established years before that 14 was optically stable 39-40). 

Optically active chochins were prepared by the Hofmann route 641 starting from (i )(—)-4-methyl[2.2]paracyclophane (38) with known chirality 54,67) (see 2.9.). Introduction of the trimethyl-ammoniomethyl group (via acetylation and subsequent transformations) afforded (—)-39 which was then cross-coupled with the ammonium base 36 to give a mixture of [2.2]paracyclophane and the levorotatory[3] and [4]chochins (40,43) with ( )-chirality in these cases the descriptors (/ ) and (5) specify the planar chirality of the inner rings(s) as shown in Fig. 2, in accordance with the rules presented in Section 1.2. 

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