Tris(pyrazolyl)hydroboratomagnesium and aluminum alkyl derivatives: alkyl exchange with methyl iodide and enolate formation with acetone

Abstract

The further conversion of 2 into the quinaldic acid moiety of 1 may involve either (a) cleavage of the N 1/C7a bond and connection of the side-chain nitrogen to C7a or (b) cleavage of the N1/C2 bond and connection of C2' to Nl. This issue was decided in favor of option (b) by feeding L-[/'«do/e-15N,l,,2,-13C2]tryptophan.26 The resulting 1 showed 13C enrichment in the carboxyl group and C2 of the quinaldic acid moiety and one-bond coupling of these two signals to each other. In addition, the QC2 signal at 143.56 ppm displayed 3.02 Hz one-bond coupling to 15N, and the QCO showed a two-bond coupling of 8.08 Hz to the 15N,28 indicating that C2' of tryptophan has been intramolecularly connected to the 15N-labeled indole nitrogen. A mechanistically reasonable pathway for the transformation of the indole to the quinoline system, which is consistent with the experimental data, is portrayed in Scheme II. This process has chemical precedent in the hypochlorite-catalyzed conversion of 2 into 4-acetylquinoline.29Acknowledgment. We are indebted to Dr. Edith W. Miles, Bethesda, for a generous gift of tryptophan synthase, to E. R. Squibb and Co. for supplying thiostrepton, to Drs. Koji Kobayashi and Motomasa Kobayashi for the chiral methionine samples, and to Kyungok Lee and Lynda Callicotte for chirality analyses of acetate samples. This work was supported by NIH research Grants AI 20264 and GM 32333 and by NIH (RR02231)-US-(24) The methionine samples used in these experiments were synthesized independently from the ones used to label 1; as a control, one of them was also shown to be incorporated into 1 with retention of methyl group configuration.(25) Zydowsky, T. M.;

Structure of hydridotris[3-(p-tolyl)pyrazolyl]boratothallium(I)

“…In connection with a study of Group VI transition metal complexes containing sterically crowded poly(1-pyrazolyl)borate ligands, we had occasion to prepare hydridotris [3-(p-tolyl)pyrazolyl]boratothallium(I), HB(p-MeC6Ha-C3H2N2)3T1 (1). Since there is little structural information available on main-group-element poly(1-pyrazolyl)borates as a class (Nicholson, 1984;Lee & Nicholson, 1986;Han, Looney & Perkin, 1989) and only a single crystallographically characterized thallium(l) derivative {the tert-butyl analogue of (1), hydridotris [3-(tert-butyl)pyrazol-1-yl]thallium(I)} (Cowley, Geerts, Nunn & Trofirnenko, 1989), we have carried out an X-ray crystal structure analysis on (1).…”

Tris(pyrazolyl)hydroboratozinc alkyl derivatives: direct comparison of the reactivity of Zn-C and Mg-C bonds

“…We have recently described the syntheses and reactivity of the magnesium alkyl derivatives [q3-HB(3-B~tpz)~]MgR (3-Butpz = 3-C3N2ButH2; R = Me, Et), in which the tris(pyrazoly1)hydroborato ligand provides a welldefined environment about the magnesium centre . 4 Here we describe the syntheses and reactivity of the monoalkyl zinc derivatives [q3-HB(3-Butpz)3]ZnR (R = Me, Et) so that direct comparisons between the reactivity of the Zn-C and Mg-C bonds may be made. F(OO0) = 984 electrons, p(Mo-K,) = 10.1 cm-', T = 295 K, crystal dimensions 0.30 mm X 0.36 mm X 0.42 mm.…”

Chemistry of the p-block elements with anionic scorpionate ligands

“…Parkin [18] reported the reaction of AlMe3 with KTp * to yield [Al(Tp * )Me2] which has been spectroscopically characterised. 1 H NMR studies [19] show single environments for both the methyl and pyrazole protons from room temperature to -90 °C.…”