Ethylmethylphenylphosphine oxide

Numerous data illustrate a third order rate dependence for this type of reaction, first order with respect to the phosphonium ion concentration and second order with respect to hydroxide ion concentration. The influence of the solvent has been studied. Optically active benzylethylmethylphenylphospho-nium hydroxide was shown to decompose stereospecifically with inversion to produce optically active ethylmethylphenylphosphine oxide. On the basis of these findings, the mechanism generally admitted is indicated in Scheme 38. 

Although ethylmethylphenylphosphine oxide was the first tetrahedral phosphorus compound to be resolved , only negative results were obtained when attempts were made to resolve methyl(a-naphthyl)phenylarsine oxide (142) by protonation and separation of (-i-)-a-bromocamphor-jc-sulphonate salts, or (c>-carboxyphenyl)methylphenyl-arsine oxide (143) or its anhydride 144 after protonation and use of (—)-brucine or (-l-)-morphine . The reversible combination of a tertiary arsine oxide with water was recognized at the outset and it is this property that is responsible for the racemization - ... 

The major product obtained by alkylation of the carbanion derived from 2-(dimethylamino)ethylmethylphenylphosphine oxide (66) is (67) rather than (68), while alkylation of the carbanion derived from ethylmethylphenylphosphine oxide (70) takes place exclusively at the methyl group.33 The former reaction provides a useful synthesis of appropriately alkylated vinylphosphine oxides (69) which are not otherwise easily prepared (Scheme 12). The N-silylated nitrile imines (72) have been prepared in solution by silylation of carbanions (71) of diazomethylphosphine sulphides.34 At room temperature compounds (72) rearrange to the isomeric diazo compounds (73). 

The absolute configuration of the major adduct 7a obtained from methyl iodide was shown to be S after removal of the organocyanoborane moiety by treatment with DABCO, oxidation of the phosphine obtained and then, comparison with the known (/ )-ethylmethylphenylphosphine oxide. 

In these early days, only quaternary phosphorus compounds were resolved. Ethylmethylphenylphosphine oxide (1) constitutes the first ever racemic F-stereogenic compound separated into individual enantiomers in 1911 by Meisenheimer and Lichtenstadt. It took 15 years for the same laboratory to repeat that feat and apply the same method to resolve benzylmethylphenyl-phosphine oxide (2). In 1944 sulfide 3 was resolved by Davies and Mann and 15 years later McEwen and co-workers" resolved the first acyclic phosphonium salt (4). 

When phosphorus is substituted with four different substituents, the resulting tetrahedral phosphonium salt is, of course,chiral. When (5)-benzylethylmethylphenyl-phosphonium iodide is treated with phenyllithium (Scheme 10.55), the corresponding benzylidenium ion results. Because this ion, on reaction with benzaldehyde, generates (i )-ethylmethylphenylphosphine oxide and ( )-stilbene, it is argued that the reaction proceeds with retention of configuration. 

SOGI2 in benzene added dropwise below 30° to a stirred soln. of ethylmethyl-phenylphosphine sulfide (prepn. s. 730) in benzene, maintained 2 hrs. at room temp., refluxed 15 min., the crude product dissolved in benzene, water added, and refluxed 1 hr. ethylmethylphenylphosphine oxide. Y 81%. F. e. s. H. J. Harwood and K. A. Pollart, J. Org. Ghem. 28, 3430 (1963). ... 

Continuing their investigation of the stereochemistry of tervalent phosphorus, Mikolajczyk and his co-worker have shown that optically active O-methyl ethyl-phenylphosphinite (112) and S -ethyl ethylphenylthiophosphinite (113) react with methyl-lithium and sodium methoxide with predominant inversion of configuration at phosphorus. The absolute configuration of (113) was established by conversion into ethylmethylphenylphosphine sulphide, and the stereochemical course of the nucleophilic displacements was determined by conversion of the initial products into the corresponding oxide and sulphides, as shown in Scheme 9. 

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