Yoshihiro Yokoyama, Y. Ohashi, Kazuyuki Umemura
Aug 1, 1998
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Analytical Sciences
Abstract
furans having an aminomethyl function on 5-position, which are obtained by the electrolytic methoxylation1 or bromine-methanol reaction2 of the corresponding furan derivative, are easily transformed into 3-hydroxypyridine derivatives. In the course of total synthesis of Karnamicin B1 (1)3, the application of the latter method (the former gave unfruitful results) on 3,4-dimethoxyfuranonitrile (2) gave exclusively an addition product of both bromo and methoxy groups. The single crystal of the addition product was obtained by slow recrystallization from an ether solution covered with hexane vapor. Here, we would like to report the results of Xray analysis to determine the position of added groups. The crystal data and experimental details are given in Table 1. All the non-hydrogen atoms were refined anisotropically. All the hydrogen atoms were located on a difference Fourier map and refined isotropically. The absolute configuration was determined with Flack’s c parameter. This indicates that the molecular configuration is S. The relation between the optical rotation and the absolute configuration of the molecule will be reported in the following paper. The final atomic parameters for non-hydrogen atoms are listed in Table 2. The bond distances and angles are listed in Table 3. The molecular structure drawn by ORTEP4 with the atomic numbering is shown in Fig. 1. The structure indicates that the methoxy and bromo groups are inserted to the 4and 5-positions, respectively. This means the product is a 1,2-addition product (4) instead of a 1,4-addition product (3). The 3-methoxy group is coplanar with the plane which consists of the cyano group and the double bond (C4–C3–O4–C8=1.4(4) ̊) and has the smallest displacement factor among three methoxy groups. The crystal structure viewed along c axis is shown in Fig. 2. The C8 atom of the 3-methoxy group is hydrogen bonded with N1 of the cyano group and O2 of the 4-methoxy group (C8...N1=3.461(4) and C8...O2 =3.473(2)Å) and the intermolecular distance Br1...C4 =3.497(2)Å is shorter than the sum of van der Waals radii. The molecules form the column structure around the six-fold screw axis through these intermolecular interactions. The C1 and C8 atoms are hydrogen bond869 ANALYTICAL SCIENCES AUGUST 1998, VOL. 14