metacyclophane 4 is thefirstofitskind to erystatlize with both bridges in the pseudo-boafconformation. Anumber ofotberunusual features arealso apparent in the crystal structure,noneofwhich arepredicted byAMlorabiniriocatcntations.
01997 Elsevier Science Ltd.
2,1l-Dithia[3.3]metacyclophanes areprominent membersof thecyclopharte familydueto theirinteresting confirmational behaviour, unusual spectroscopic properties, transrmnularinteractions and their utility as precursorsto [2.2]metacyclophanesand [2.2]metacyclophane-1,9 -dienes.1 For the latter reason,we required syrs-6,15-dicyano-2,1 l-dithia[3.3]metacyclophane as a syntheticintermediatein connectionwithongoingstudies of n.2.2cyclophanes ("tethered[2.2]metacyclophanes")2 and npyrenophanes.3
Thesynthesis(Scheme1)startedwith5-cyano-m-xylene 1,whichwasbrominatedwithNBS/AIBN/hv to afforddibromide2 in 40%yield. Conversionof 2 intodithiol3 proceededin only48%yield,presumablydueto partialhydrolysisof the nitrile functionduringthe basehydrolysisof the intermediatebis-isothiouroniumsalt. Highdilutioncouplingof 2 and 3 producedthe dithiacyclophane44in 77% yield. In order to circumventthe problemsassociatedwith the hydrolysisstep, the self-couplingof 2 usingNa2S/A12035 was investigatedas an alternaterouteto 4. Analysisof the 300MHz IH NMRspectrumof the crudeproductindicatedthat 4 hadbeen formedin the typical50-60%yield. However,separatingit fromthe correspondingcyclic timer provedto be verydifficult. Careful,repeatedchromatography afforded25%of pure4. The internalprotons(Hi)of 4 appear at 87.31 in its 300MHzIH NMRspectrum,indicatingthatthe moleculeadoptsthe expectedsynconformation in sohrtion.6Thebridgeprotonsappearasasingletat53.72.