Cobalt‐Catalyzed Cycloaddition of Alkynes and Nitriles to Pyridines: A New Route to Pyridoxine (Vitamin B6)
A new synthesis of pyridoxine hydrochloride (1) based on a Co‐catalyzed cycloaddition of MeCN with substituted di(2‐propynyl) ethers (3 and 16) is described. The reaction sequences following cycloaddition and leading to 1 involve as key steps the rearrangement f the pyridine‐N‐oxide 6 to the 3‐hydroxypyridine 7 with Ac2O and a modified Curtius rearrangement of the acid 19 and subsequent diazotation and hydrolysis to the same pyridoxine precursor 7, respectively. The intermediate 7 is transformed to 1 by well‐known procedures.
Summary.A general review is given of the UV.-spectroscopic properties of some simple molecules containing the N-N and N-0 bond, respectively. The electronic structure of nitrosomethane, azomethane, trimethylamine oxide, azomethane N, "-dioxide, nitromethane, methyl nitrite are reinvestigated by the SCF-CI method, within the frame of thc all-valence CNDO procedure. These calculations confirm a number of older assignments, but also allow predictions concerning some not settled questions. For instance, nitroalkanes should exhibit not one but two %-n* transitions, namely a t 275 nm and around 350 nm. This prediction agrees with conclusions by Djerassi and 4-0-workers on the spectra of some nitrosteroids.Particular attention is given to the symmetry and relative energetic position of nonbonding orbitals. The question of "basicity" and "ease of protonation" is discussed in relation to it. Calculations on the overall charge distribution complement this investigation.Kein Element zeigt in der organischen Chemie eine solche Vielfalt von Bindungsarten wie der Stickstoff. Er geht Einfach-, Doppel-und Dreifachbindungen mit Kohlenstoff eiii ; er bildet Einfach-, Doppel-und Dreifachbindungen mit sich selber. Eine auffallende Mannigfaltigkeit von verschiedenen Bindungsverhaltnissen findet man in Molekeln, welche zusatzlich noch Sauerstoff enthalten, insbesondere StickstoffSauerstoff-Bindungen aufweisen. Zwar bildet die Chemie der Nitroxyle, der Nitrosoverbindungen rind ihrer Dimere, -als Oxydationsprodukte von Azoverbindungen aufzufassen -, deir Oxime, der N-Oxide, der Nitroverbindungen und Nitrile ein etwas spezielles Gebiet, fur den Biochemiker vielleicht von sekundarem Interesse. Vom Standpunkt der Bindungslehre und der Molekelspektroskopie aus aber erweist sicli dieses Feld als umso fruchtbarer. Es scheint angebracht, die Eigenschaften der Nitroxyle und Nitrosoverbindungen mit denjenigen von NO, die Merkrnale der Nitroverbindungen mit denjenigen von NO, in Zusammenhang zu bringen 111. Daher bildet eine kurze Betrachtung dieser einfachsten Molekeln den Ausgangspunkt unserer Untersuchung.
The 13C‐NMR.‐spectra of 7,8‐dihydropterines and 5,6,7,8‐tetrahydropterines show a large difference in the chemical shifts of the 4a‐ and 8a‐sp2‐carbon atoms. From the CNDO calculations it is apparent that there is a considerable difference in electron density at C(4a) and C(8a) atoms, which leads to a strong polarity of the CC‐Bond. The electron distribution in the highest occupied molecular orbital (HOMO) is discussed.
The rotational strength of the longest‐wavelength electronic transition in some simple γ‐lactams and some related isoelectronic molecules is calculated using the CNDO‐CI method. Qualitative agreement with experimental values is obtained. In all investigated systems the long‐wavelength transition corresponds to the nπ* transition. A quadrant rule seems to hold for this transition.
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