Trans‐Selective Olefin Syntheses

Abstract

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 ...

Preparation of New Phosphoranes by Chemoselective Reaction of Acetylenic Esters with Compounds Containing Two Nitrogen Atoms

“…31a Acetylthiourea was also prepared from the reaction of acetyl chloride and ammonium thiocyanate according to the reported procedure in the literature. 31b The chemoselective reaction of dimethylacetylenedicarboxylate (2) and N-ethyl-N'-propionylurea (1) in the presence of PPh 3 , produced products which were characterized as phosphoranes (3a-b) on the basis of spectral data (Scheme 1). The probable mechanistic pathway that best explains the synthesis of these compounds, is depicted in Scheme 2.…”

Palladium‐Catalysed Cross‐Coupling Reactions of Triorganoindium Reagents with Alkenyl Halides

“…(Z)-Undec-5-ene (5): [29] According to the general procedure, the reaction of 1 (238 mg, 1.062 mmol) with tri-n-butylindium (Z)-Nona-1,3-diene (6): [30] According to the general procedure, the reaction of 1 (215 mg, 0.959 mmol) with trivinylindium (0. [(Z)-Non-3-en-1-ynyl]benzene (7): [31] According to the general procedure, the reaction of 1 (240 mg, 1.071 mmol) with tris(phenyl- non-3-en-1-ynyl]silane (8): [32] According to the general procedure, the reaction of 1 (261 mg, [(E)-Hept-1-enyl]benzene (9): [27] According to the general procedure, the reaction of 2 (230 mg, (E)-Oct-2-ene (10): [33] According to the general procedure, the reaction of 2 (224 mg, 1.000 mmol) with trimethylindium (0. (E)-Undec-5-ene (11): [29] According to the general procedure, the reaction of 2 (232 mg, 1.035 mmol) with tri-n-butylindium (E)-Nona-1,3-diene (12): [30] According to the general procedure, the reaction of 2 (210 mg, 0.937 mmol) with trivinylindium (0.…”

Enantiomerically Pure Vinylcyclopropylboronic Esters

“…First, we tested the Schlosser reaction [21] starting from aldehyde 8; this procedure led to the olefin 10b, albeit in poor yield and selectivity (Scheme 4). However, by altering the bases used for the two consecutive steps (from phenyllithium to n-butyllithium) as well as the equivalents used (from 2 to 1 equiv.…”