Oxiranes alkylation with

The Darzens reaction between aldehydes and ketones with activated halomethyl compounds is an effective route to oxiranes under phase-transfer catalytic conditions and the catalyst has a profound stereochemical control of the substituents (see Chapter 12). The reaction has been conducted in high yield under liquidtliquid and solidrliquid two-phase conditions with a range of halomethyl compounds [e.g. 25-30], Ketones tend to be much slower in their reaction and benzylic ketones undergo alkylation with chloroacetonitrile in preference to the Darzens reaction [25]. 

All acetylenes with a terminal triple bond are instantaneously converted into the alkali acetylides by alkali amides in liquid ammonia. For many alkylations with primary alkyl halides liquid ammonia is the solvent of choice and the functionalization with oxirane can also be carried out in it with good results. Reactions of ROOM with sulfenyladng agents (R SSR1, R SON, R SSC R ) or elemental sulfur, selenium or tellurium are mostly very successful in ammonia, the same holds for the preparation of ROC1 from RC=CM and iodine. The results of couplings with carbonyl compounds are very variable. 

Alkylation with oxiranes gave, by analogy, enantiomerically pure l-phenyl-l,3-diols4. The method was reviewed recently5. 

Styrene, one of the world s major organic chemicals, is derived from ethylene via ethylbenzene. Several recent developments have occurred with respect to this use for ethylene. One is the production of styrene as a co-product of the propylene oxide process developed by Halcon International (12). In this process, benzene is alkylated with ethylene to ethylbenzene, and the latter is oxidized to ethylbenzene hydroperoxide. This hydroperoxide, in the presence of suitable catalysts, can convert a broad range of olefins to their corresponding oxirane compounds, of which propylene oxide presently has the greatest industrial importance. The ethylbenzene hydroperoxide is converted simultaneously to methylphenyl-carbinol which, upon dehydration, yields styrene. Commercial application of this new development in the use of ethylene will be demonstrated in a plant in Spain in the near future. 

N-Alkylation with Ethylene Oxides (Oxiranes) or Aziridines... 

A review of the IR frequencies of the three-membered heterocycles is found in Katritzky and Ambler. The IR frequencies were more recently studied by Potts. " George recorded the IR spectra of 16 straight-chain oxiranes for analytical purposes and reported their refractive indices too. IR (4000-200cm" ) and Raman spectra have been taken in the solid and the liquid phases for the conformational examination of alkyl-substituted oxiranes. Studies have been made of the steric structure of oxirane-carboxaldehydes and the low-temperature oxidation of cyclohexene in the presence of Co" chelates. Analyses have been carried out on the IR spectra of oxiranes in the region of 850 cm" and the vibrational energy levels. Steroid oxiranes have likewise been subjected to IR investigation. Hirose published the rotational spectra of 10 oxiranes together with their evaluation and, in conjunction with the microwave spectra, determined thero,r, andr, structures of the compounds. 

Krief et al. have shown that selenium ylides behave as their sulfur analogues and convert a variety of carbonyl compounds to oxiranes <89H(28)1203>. The latter compounds can be directly obtained by using R2Se=CHR /i-hydroxyalkylselenides (available from carbonyl compounds by addition of RSeCH2Li) may serve as suitable precursors as well, either in a two-step protocol, via the selenonium salt by alkylation with magic methyl (MeS03F), or directly by treatment with thallous ethoxide in chloroform. Oxidation of the /t-hydroxyalkylselenides with peracid, followed by treatment of the resulting selenone with base, results in oxirane formation (Scheme 60). 

By far, the most widely used method is the alkylation of an a-sulfonyl carbanion followed by reductive removal of the sulfonyl group. Different electrophiles such as alkyl halides, sulfonates, sulfinates, acetates, oxiranes, and electron-deficient multiple bonds are employed for the formation of the new C-C bond. Palladium-catalyzed it-allylic alkylation with a-sulfonyl carbanions is also a commonly used method. After the C-C bond formation, the conditions for the final desulfonylation reaction with the appropriate reagent will depend on the structure of the sulfone intermediate. 

In a number of derivatization reactions it is advisable to replace the original counter ion by another one. As mentioned in Sects. II-6 and II-9, organolithium compounds give much better results than potassium compounds in reactions with enolizable carbonyl compounds and with sulfur, selenium and tellurium. On the other hand, alkylations with alkyl halides and with oxiranes proceed more smoothly with the potassium intermediates. Although HMPT may be used as a co-solvent, simple replacement of lithium by potassium may give similar results combination of the counter ion and solvent effects may be even better. The replacements Li+ K + and K+ Li+ are generally fast reactions in a wide temperature range (compare e.g. [161,241]) ... 

For the conversion of 280— 281, two alternative methods were developed. The first consists of the opening of the oxirane ring with dimethylamine that leads to alkyl 3,4-dideoxy-3-dimethylamino-DL-glycopyranoside (355). Oxidation of 355 to N-oxidc (356) and its thermal degradation gives 281 in 50-70% yields. 

Phosphonium salts are produced by acidification of an appropriate ylid (6.422) or by adding halophosphines or alkyl halides to ylids (6.377, 6.378). Phosphonium cations are obtained by reacting phosphorus pentachloride with phosphorus pentaphenyl (6.477) or with lithio biphenyl (480). Oxiranes react with phosphines to produce betaines which, in the presence of acids, give hydroxy-alkyl phosphonium salts (3.114). 

Oxiranes are highly toxic alkylating agents and the hydrolysis product of ethylene oxide ethylene glycol and reaction products of oxiranes with chloride ions is likewise toxic. The latter reaction yields 2-chloroethanol, which arises from oxirane, and isomeric vicinal chloropropanols (chlorohydrins) resulting from methyloxirane (Figure 11.3). Oxiranes react with a number of other food components, such as vitamins (riboflavin, pyridoxine, niacin and folic acid) or amino acids (methionine and histidine) to form biologically inactive products. 

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