Chemistry of Acronycine, II. Dimerization of Noracronycine

Chemistry of Acronycine: III

“…this latter signal appeared at ö 7.447 (d, 1H, J = 8.6 Hz) and in AB-2 (4) at ô 7.420 (d. iH, J = 8. 4 Hz, C-li'H) and Most of the features of the 'H NMR spectrum of AB-3 could now be assigned with certainty. A singlet aromatic proton (ô 6.348, C-5H), a pair of doublets (ô 5.045, C-2"H and ô 6.085, C-1"H), three sets of geminal methyl signals ( 0.496, 13'-CH3, ô 0.560, 13"-CH3, 0.962, 14'-CH3, ô 1.039, 14"-CH3, andö 1.508 and 1.642 (13-CH3 and 14-CH3), and one of the three hydrogen-bonded phenolic protons (ô 14.256 C-6-OH) were assigned by comparison with the 1H NMR spectra of noracronycine 2and AB-1 3.…”

“…However, only one aromatic singlet (at ô 459 (d, 1H, J = 8.7 Hz, C-1OH. But in the 1H NMR spectrum of AB-i (3) these signals appeared at 6.907 (d, 1H, J = 8.5 Hz, C-11H) and 7.413 (d, 1H, J = 8.7 Hz, C-11'H) [4]. That is, the signal at ö 6.907 from the upper unit appeared about 0.5 ppm higher than that in the lower unit (ô 7.413), and also 0.51-0.55 ppm higher than those signals in noracronycine and AB-2.…”

“…Unambiguous 'H NMR assignments for AB-i and AB-2 were achieved through the use of decoupling and nOe techniques [4] and are given in 3 and 4, respectively. In the 'H NMR spectrum of AB-3, there are three doublets which could be assigned to the aromatic protons pen to the N-CH3 groups, namely the signals at 6.734 (d, 1H, J = 8.4 Hz), 6.802 (d, 1H, J = 8.5 Hz) and 7,373 (d, iH, J = 8.7 Hz).…”

“…It remained to establish the assignments with a particular unit within the molecule. One set of the three aromatic protons, 6c, was assigned to the lower unit on the basis of a comparison between C-ii"H and the corresponding proton in AB-1 (3) [4].…”

“…We have previously described a more detailed study of this reaction [41 and found that noracronycine (2) and two dimeric species, AB-1 (3) and , were the most abundant products. The structures of the dimers were deduced through examination of 1H NMR spectral data and single crystal X-ray crystallographic analysis [4]. Improved yields were obtained when 2 was the starting material.…”