Abstract. In our technical synthesis of vitamin A, the intermediate P-C,,-ketone (5) is obtained in a four-step sequence from p-ionone (1). In order to reduce the number of reaction steps, 1 is condensed with a C,-fragment, leading to a convergent synthesis of 5. The title compound (8) with R = -CH(OC,H,)-CH, (Si) is prepared by the reaction of 1,3-dichloro-2-propanol with ethyl vinyl ether, followed by dehydrohalogenation, substitution and isomerisation of the resulting mixed acetal (17i) in a simple one-pot procedure by treatment with sodium acetylide. The syntheses of several C,-synthons of type 8 with different groups R are described. The condensation product of 1 and 8i is partially hydrogenated and subsequently hydrolysed to 5 in an overall yield of 85 %.
A solution of 33.0 g (0.33 mol) of methyl cyanoacetate in 1,2-dimethoxyethane (DME, 60 ml) was added drop by drop in 10 min to a suspension of 8.0 g NaH in 40 ml of DME, cooled in ice. After 1 hour to this reaction mixture a solution of 29.3 g (0.167 mol) of A in 75 ml DME was added, also dropwise. at a temperature of 20-25". I f hours later this reaction mixture was poured into dilute hydrochloric acid. After extraction with CH,CI, the extract was washed with water until neutral and dried over MgSO,. The solvent was evaporated and the product crystallised from methanol. Yield of B 32.0 g (82%). M.p. = 166.3 -167.2O. 60 and I 0 0 MHz spectra were run on a JEOL C-60-HL and a JEOL 4H-100 spectrometer. The chemical shifts, 6. are expressed in ppm downfield to TMS. The relaxation measurements were performed on a home-built 75 MHz proton NMR spectrometer". The strength of the R F field during the pulses was 10 Hz. T , values were determined using the CPGM program with 180" pulse distance in the range 0.3 to 0.9 s. T , values were determined using the 180-r-90 program. Selectivity in the T , and T, measurements was obtained using a filtering method lo. Heteronuclear decoupling experiments were performed by Dr. A . J . de Hoog (RU, Leiden) on a JEOL PS-100 NMR spectrometer, and by Mr. C . Kruk (GU, Amsterdam) on a Varian XL-100-15 instrument. I4N spectra (in order to determine T, from the linewidth) were run by Dr. P. R. Locher (Philips Research Laboratories, Eindhoven) on a Bruker BKR-321 spectrometer. N M R solvents were carefully dried on mol sieves to avoid exchange of the chelate proton with traces of water. Samples for relaxation measurements were carefully degassed using the usual freeze-pumpthaw technique. The temperature was varied by standard techniques and chacked with a calibrated thermocouple directly inserted in a sample tube. I R spectra were run on a Perkin Elmer 457 spectrophotometer.Abstract. ' H-NMR evidence is presented for the covalent hydrazination of 1 -methyl-, 1,2-dimethyl-, 1,4,6-trimethyl-and 1-methyl-4-phenyl-pyrimidinium iodide (la-d) at C(6). With fully deuterated hydrazine hydrate the salts l a d undergo ring contraction into pyrazole and pyrazole derivatives (8a-d) containing deuterium at position 4. Evidence is presented for the intermediacy of a tautomeric mixture of open-chain compounds, in which H/D exchange occurs before cyclisation takes place.N-Methylpyrimidinium salts undergo ring contraction intL pyrazoles on treatment with hydrazine at room temperature3. It has been proposed that the ring contraction starts by an initial formation of the o-adduct 1,6-dihydro-6-hydrazino-I-methylpyrimidine which undergoes a subsequent ring opening. Although there is ample NMR evidence for the formation of a 1 : 1 covalent o-adduct from quaternised azines, diazines and triazines with liquid ammonia4*', the formation of a o-adduct with hydrazine has never been observed. In this report we present the first unambiguous NMR evidence for the existence of a covalent o-adduct between I-methylpyrimidinium...
Die 1,3‐Dichlor‐2‐Alkoxypropane (I), deren Synthese angegeben wird, reagieren mit Natriumacetylid zu den Titelverbindungen (II).
Mittels 1H‐NMR‐spektroskopischer Untersuchungen wird gezeigt, daß die Reaktion aller vier Salze (I) mit perdeuteriertem Hydrazinhydrat bei ‐l 5 bis ‐30°C unter kovalenter Hydrazinierung am C‐6 mit Bildung der Produkte (II) verläuft, die infolge Ringkontraktion und Verlust . der Formamidine (IV) in die in 4‐Stellung deuterierten Pyrazole (III) übergehen.
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