is removed in a vacuum and the residue is taken up in 200 ml of 0.1 % aqueous hydrocyanic acid and added t o a column (40 mm diameter by 100 mm) of carboxymethylcellulose.Most of the unchanged cyanocobinamide runs through the column; the rest is eluted with 2 % acetic acid, and immediately thereafter the cobyric ester (3) of 1-aminopropan-2-01 is eluted with a 1 : l mixture of 2 % acetic acid and 2 % ammonium acetate solution. This ester is purified by extraction with phenol[3J, taken up in 100 ml of water, and acetylated by slow, dropwise addition to 5 ml of acetic anhydride at 0 to 2°C with stirring. After an hour the product is washed twice with 10 ml of chloroform, and the corrinoid is purified by extraction with phenol. For cleavage, the ester is kept at 0°C for 2 h in 200 ml of 1 M aqueous piperidine solution. The mixture is washed three times with 30 ml of 2:1 isopropyl ether/l-butanol and brought to p H 5.5 by dilute hydrochloric acid. After a further phenol extraction and cellulose-column-chromatography with sec-butanoli water (10: 3) the cobyric acid is obtained in pure form; yield 20-22 %.Usually only mixtures of trans-and cis-olefins can be obtained by the Wittig reaction. A few examples are known yielding predominantly trans- [ I ] or cis-[21 olefins. trans-Selective olefination can be expected if equilibration of the erythro-and threo-betaines ( 1 ) [ I d can be accelerated.We have now found that interconversion of the diastereoisomeric betaine ylides (2) [31 is extremely rapid [4J. These ylides are formed if the betaine-LiX adduct ( I ) is treated with phenyl-lithium or n-butyl-lithium in ether/tetrahydrofuran (1 : 1) at -30 "C, and with proton donors (e.g., hydrogen chloride or t-butyl alcohol) they regenerate the betaine-LiX adducts ( I ) .( I ) . erythro + threoThe equilibrium between the diastereoisomeric betaine ylides lies far to the side of form (2b), so that protonation gives mainly the threo-betaine [threo-(I)]. Subsequent treatment with potassium t-butoxide then liberates almost pure transolefin (cf . Table). Olefin 2-Octene 2-Octene 4-Octene 1 -Phenyl-1 -propene 1-Phenyl-1 -butene 1 -Phenyl-1-hexene 1 -Phenyl-1,3-pentadiene 2-Phenyl-2-butene R I R trans: cis 99: 1 96: 4 98: 2 99: 1 97: 3 96: 4 97: 3 8 9 : l l -[a] Determined gas-chromatographically.[bl Isolated in substance.[c] With acetophenone as carbonyl component, i.e., R = G H s and with CH3 in place of H. ProcedureThe phosphonium salt (30 mmole) is suspended in 50 ml of tetrahydrofuran and 30 ml of ether and stirred with 30 mmole of ethereal phenyl-lithium solution until the Gilman test is negative (about 10 min). The solution is cooled to -70 OC and 30 mmole of aldehyde (dissolved in 20 ml of ether) is added; the mixture is stirred vigorously. As soon as decolorization is complete (5 min at -70 to -4OoC), a further 30 mmole of phenyllithium solution is added and the whole kept at -30 "C until the Gilman test is again negative (about 5 min). This solution is treated with 33 mmole of ethereal hydrogen chloride and with 45 mmole of ...
Nicht-stabilisierte Phosphor-Ylide und ihre Betaine lagern Lithium-Salze an und biiBen dabei ihre ursprungliche Reaktivitat gr6Rtenteils ein. Mit Kalium-text.-butanolat lassen sie sich wieder aktivieren. Je nach Bedarf kann man somit die Wittig-Reaktion abbremsen und erneut beschleunigen. -HLufig fuhrt die Carbonyl-Olefinierung zu einem Isomerengemisch mit ca. 50 % cis-bzw. trans-Olefin. Darin auRern sich zwei gegenlaufige Effekte: 1) Phosphor-Ylide und Aldehyde vereinigen sich unter kinetischer Kontrolle bevorzugt zum erythro-Betain und liefern, wenn man die Betain-Bildung irreversibel macht, iiberwiegend cis-olefin. 2) Thermodynamisch ist das threo-Betain stabiler, so daR bei rascher Einstellung des Diastereomeren-Gleichgewichts zwischen erythro-und threo-Betain hauptsachlich trans-Olefine entstehen. -Praparative Methoden zur cis-oder trans-selektiven Carbonyl-Olefinierung werden beschrieben. EinfiihrungDie Phosphor-Ylide lassen sich in Mesomerie-stabilisierte und nicht-stabilisierte unterteilen 1). Phosphor-Ylide, die in a-Stellung mit Estergruppen, dem Nitril-Rest oder anderen stark elektronegativen Funktionen substituiert sind, konnen isoliert werden und sind an der Luft bestandig. Zwischen den ,,stabilen" Yliden und den ,,reaktiven" Yliden vom Typ des Triphenylphosphonium-methylids stehen die maRig Mesomerie-stabilisierten Ylide, z.B. Triphenylphosphonium-benzylid oder Triphenylphosphonium-chlormethylid. Zu dieser Gruppe zahlen wir alle Ylide (HsC&P -CH -R, wenn die zugehorige Kohlenstoffsaure H3C -R einen pK-Wert von 35 -37 in der McEwen-Skala2) einnimmt, und bezeichnen sie als ,,moderierte" Phosphor-Ylide. e e
However, many side reactions occur, in contrast to the cyclization of nitrosouracils. When, for instance, a solution of 4-methylamino-5-p-nitrobenzylideneaminouracil(Ia) in nitrobenzene is refluxed for only a short time (2-5 min), fractional crystallization of the product leads to a 40 % yield of 7-p-nitrobenzyltheophylline (2a) and a 12 % yield of 8-p-nitrophenylisocaffeine (3a). Since the Schiff bases (Ib)-(Id) also afford 7-benzyltheophyllines (2b)-(2d) as main products in yields around SO%, the reaction must proceed by attack of the alkyl substituent on the 4-amino group onto the azomethine portion of the molecule. This is thus a new type of imidazole ring closure. Cyclization in Traube's sense can be achieved by the use o f aqueous alcohol in presence of CU(II) ions as solvent, instead of nitrobenzene. Compound (3a) is formed from ( l a ) in 61 % yield after only 5 minutes' boiling. The reactiondetermining factor is probably complex formation between the Cu and the azomethine group. A novel purine ring closure was also found jn the cyclization of 4-alkylamino-1,3-dimethyl-5-phenylazouracil (4). If the derivative (4. )is boiled in nitrobenzene for about 4 hr under reflux, theophylline ( 5 4 is obtained in 50 % yield;heating of the compound (46) alone above its melting point gives 8-methyltheophylline. In both cases the a-C atom of the substituent on thz 4-amino group enters into reaction and appears as C-8 in the purine derivative.
Versetzt man eine im Nz-Stromsiedende Suspension eines Perthiophosphonsaureanhydrids in Benzol mit 2 Mol n-Tributylphosphin (z. B. 5 g [ C~H~P S Z ]~, 5,9 g (n-C4H9)3P, 50 in1 Benzol), so tritt nach ca. 5 Minuten vollstandige Losung ein. Beim Abkuhlen des Gemisches, eventuell nach Einengen dcr Losung, werden farblose Kristalle abgeschieden, die nacb dem Waschen rnit wenig Benzol analysenrein sind. Die entstehenden Verbindungen (2) sind als innere Phosphoniumsalze aufzufassen, die resonanzstabilisiert sind. Sie sind an der Luft bestandig und liegen nach kryoskopischen Molekulargewichtsbestimmungen in Benzol, Bromoforni und Nitrobenzol monomer vor. Die 3lP-NMR-Spektren zeigen zwei Dubletts mit Kopplungskonstanten, die fur P-P-Bindungen charakteristisch sind.
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