Methyloxirane synthesis

Procedure 2 Synthesis of Racemic 1-Benzyloxymethyl-l-methyloxirane from 3-Benzyloxy-2-methylpropene... 

Procedure 3 Synthesis of (/f)-3-Benzyloxy-2-methylpropane-l,2-diol from Racemic 1-Benzyloxymethyl-l-methyloxirane... 

The synthesis should be carried out in a wel1-venti1ated hood. CAUTION Methyloxirane ie a suspected carcinogen for fnmans. 

Of common interest in this area are predominantly hexafluoroacetone (HFA, a gas), because of its chemical reactivity as an intermediate and the solvent power of its liquid or low melting hydrates, and perfiuoro(methyloxirane) (perfiuoropropylene oxide, HFPO, a gas), used as an intermediate and building block with many applications for functional oils and polymers.1 Hexafluoroacetone is used for the synthesis of 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP), pharmaceuticals, agrochemicals and polymers. Toxic properties of some species are listed in Tabic 10. 

Due to their industrial applications, tetrafluorooxirane and perfluoro(2-methyloxirane) are the most frequently mentioned epoxides in the literature, and a number of methods have been developed for their synthesis. Although the epoxidation of perfluoroalkenes with hydrogen peroxide in alkaline media appears to be the most general method for the synthesis of per-fluorinated epoxides, it cannot be used in the preparation of tetrafluorooxirane due to the hydrolytic decomposition of the alkene. 

Current commercial production of methyloxirane (propene oxide), used extensively in the production of polyurethanes, is usually based on a chloro-hydrin process. However, the direct gas-phase synthesis of methyloxirane... 

R)-( + )-Methyloxirane, a useful chiral intermediate, has been employed in the synthesis of a variety of natural products. It is readily prepared in multi-gram quantities from ethyl L-lactate via tosylate 120b [53,54]. Reduction of the ester proceeds quantitatively with diborane over a period of 5 days to afford ( S)-( + )-propane-l,2-diol 2-tosylate (146). Cyclization with KOH gives epoxide 147 with 97% inversion of configuration. 

On addition of ethers or Bu"Li to alkenyldialkylalanes the reactivity of the latter compounds is enhanced, and they may be used to transfer a nucleophilic alkenyl unit to an oxiran. Optically active methyloxiran has been employed in a reaction of this type as part of a stereoselective synthesis of (R)-recifeiolide. ... 

It took another 35 years until the first (and still the only known) enantioselective total synthesis of (/ )-ochratoxin a (326), and therefore of ochratoxins A and B, was published by Gill et al. in 2002 (264, 265). Scheme 6.1 shows six steps of the nine-step synthesis, which was achieved with 10% overall yield. The first three steps of the procedure are not shown and comprise the preparation of 327 from (/ )-2-methyloxirane according to ref. (266). Ketene dimethyl acetal and acetylenic ester 327 react in an intermolecular cycloaddition to give 328. This diene undergoes a Diels-Alder reaction with methyl propiolate to yield 329. Lactonization ( 330), demethylation ( 331), chlorination ( 332), and methyl ester cleavage finally furnished enantiomerically pure ochratoxin a (326) (267). 

The synthesis of dichloronorcarane from cyclohexene by the chloroform-base-PTC method has been improved further as has the preparation of a-halogeno-aP-unsaturated ketones via em-dihalogenocyclopropanes by employing trimethylsilyl vinyl ethers rather than ethyl vinyl ethers. The formation of gem-difluorocyclo-propanes proceeds in high yield (60— 90%) when chlorodifluoromethane is treated with halide ion and an epoxide in the presence of an olefin. The epoxide-halide ion combination is employed to produce a base of sufficient strength, and in sufficient concentration, to maximize the production of difluorocarbene oxiran and chloro-methyloxiran afford the most suitable bases when treated with chloride ion (Scheme 4). 

Assume that a ketone is the synthetic equivalent for 53 and a bromide is the synthetic equivalent for 54. Show a synthesis of 52 from these equivalents. Now show a disconnection and synthesis of the ketone from 2-methyloxirane and a synthesis of the bromide from propyne. 

Mono- and disaccharides are highly hydrophilic substances. They are produced in large volumes, are available in highly pure form, and are relatively cheap [4,5]. They may be, and indeed have been, used as hydrophilic substrates for the synthesis of nonionic surfactants. In 1999, the worldwide production of the latter was about 3.6 3.8 million metric tons, i.e., approximately 38% of total surfactant production [6]. The majority of the conventional nonionic surfactants are oligooxyethylene (and oxypropylene) chain-containing compounds obtained in the reaction of oxirane (ethylene oxide) or methyloxirane (propylene oxide) with hydrophobic intermediates that contain a functional group with an active hydrogen atom [7]. Only recently, the direct reaction of oxirane with fatty acid methyl esters in the... 

N-tosylimino-oxysulphurane. This ylide reacts in high yield with carbonyl compounds to afford oxirans in a reaction analogous to that effected by sulphonium or oxysulphonium ylides. Optically active phenylmethylsul-phoximine could be tosylated and converted into an ylide with sodium hydride in DMSO, and it reacted with acetophenone to afford optically active 1-phenyl-1-methyloxiran. The ylide (156 R = R = Me) also effected additions to conjugated carbonyl compounds, such as co-benzoylstyrene, to afford l-phenyl-2-benzoylcyclopropane. Johnson recently has reviewed the use of N-tosyliminosulphoxonium ylides in organic synthesis. 

Propene oxide (methyl oxirane) is used on a large scale for the production of polyurethanes and is usually made using a chlorohydrin process. A greener alternative would be to use the direct gas-phase synthesis of methyloxirane from propene, using molecular oxygen in the presence of... 

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