Furan protonation

Dioxacorroles are 18-7r-electron aromatic systems like corroles. They exhibit basicity intermediate between that of porphyrin and corrole, and require 1 h at 100 °C in TFA for complete deuteration of the meso positions. The furan protons are also substituted by deuterium under the same conditions after lOOh. Friedel-Crafts acylation occurs at C-5 while alkyl halides attack on the pyrrolic nitrogens to give a mixture of mono- and di-alkyl derivatives. 

Multilayered cyclophanes have been prepared that show much the same properties regarding strain or rotation of furan units examples include 165278 and 166.279 New features emerge from studies of compounds like the [2.2] (l,4)naphthaleno(2,5)-furanophane (167) in which rotation of the furan units is possible while there is yet a strongly preferred conformation in the case of 167 the anti form shown. As a result, the naphthalene proton Hb suffers rather strong shielding by the furan ring and its resonance moves upheld by about 0.9 ppm, whereas the furan proton Ha is not much affected.271 The NMR results have been confirmed by an X-ray diffraction... 

The signals for the furan protons are again found in the region of benzenoid protons. The C-2/C-3 bond, in contrast, behaves chemically rather hke a localized olefinic double bond, that is, it undergoes addition reactions. 

Opposite to many other examples studied earlier in case of alkaloid sulfoxides in question the reaction does not show high stereospecificity and both possible isomers ars formed. They could be separated and assignments of the configurations to both isomers could be given by interpretation of NMR spectra since in each pair of isomers obtained from neothiobinupha-ridine, thiobinupharidine and thionuphlutine only one has the acetoxy group very close to the furan protons which causes different values for the observed chemical shifts in isomeric acetoxyderivatives. 

The two furan protons resonate at relatively low field, 5 7.25 and 6.50 p.p.m. (doublets, J = 2Hz), in agreement with the presence of further unsaturation conjugated with the heterocyclic moiety. A signal centred at 5 6.26 is in accordance with the presence of conjugated CH = CH. The n.m.r. spectrum also displayed signals for two tert-... 

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