Ethylene oxide, reaction with Grignard

A further complication in the reaction of Grignard reagents with epoxides is that isomeric products are often formed. Thus ethylene oxide reacts with n-butylmagnesium bromide to give a mixture of 1-hexanol and 2-hexanol 25... 

We saw an example of nucleophilic ring opening of epoxides in Section 15 4 where the reaction of Grignard reagents with ethylene oxide was described as a synthetic route to primary alcohols... 

Benzyl chloride readily forms a Grignard compound by reaction with magnesium in ether with the concomitant formation of substantial coupling product, 1,2-diphenylethane [103-29-7]. Benzyl chloride is oxidized first to benzaldehyde [100-52-7] and then to benzoic acid. Nitric acid oxidizes directly to benzoic acid [65-85-0]. Reaction with ethylene oxide produces the benzyl chlorohydrin ether, CgH CH20CH2CH2Cl (18). Benzylphosphonic acid [10542-07-1] is formed from the reaction of benzyl chloride and triethyl phosphite followed by hydrolysis (19). 

The Grignard reagent from 2-thenyl chloride can be obtained by the use of the "cyclic reactor.However, rearrangement occurs in its reaction with carbon dioxide, ethyl chlorocarbonate, acetyl chloride, formaldehyde, and ethylene oxide to 3-substituted 2-methylthio-phenes, Only in the case of carbon dioxide has the normal product also been isolated. 

Grignard reagents react with oxetane, a four-membered cyclic ether, to yield primary alcohols, but the reaction is much slower than the corresponding reaction with ethylene oxide. Suggest a reason for the difference in reactivity between oxetane and ethylene oxide. 

The addition of Grignard reagents to aldehydes, ketones, and esters is the basis for the synthesis of a wide variety of alcohols, and several examples are given in Scheme 7.3. Primary alcohols can be made from formaldehyde (Entry 1) or, with addition of two carbons, from ethylene oxide (Entry 2). Secondary alcohols are obtained from aldehydes (Entries 3 to 6) or formate esters (Entry 7). Tertiary alcohols can be made from esters (Entries 8 and 9) or ketones (Entry 10). Lactones give diols (Entry 11). Aldehydes can be prepared from trialkyl orthoformate esters (Entries 12 and 13). Ketones can be made from nitriles (Entries 14 and 15), pyridine-2-thiol esters (Entry 16), N-methoxy-A-methyl carboxamides (Entries 17 and 18), or anhydrides (Entry 19). Carboxylic acids are available by reaction with C02 (Entries 20 to 22). Amines can be prepared from imines (Entry 23). Two-step procedures that involve formation and dehydration of alcohols provide routes to certain alkenes (Entries 24 and 25). 

In the example shown, reaction of a Grignard reagent with the epoxide electrophile ethylene oxide proceeds as expected, and after acidification results in formation of an alcohol that is two carbons longer than the original nucleophile. 

The characteristic ease with which ethylene oxides undi ruu nucleophilic attack or isomerization in tbe presence of Lewie acids made them obvious substrates for tbe org nometallic reagents intro duoed by Grignard 07 around the turn of the century, and subsequently named in his hunor. The earliest disclosure of a reaction between an epoxide and a Grignard reagent, however, bears the name of Blaise,1 who noted the formation of ethylene bromohydrin on troii merit of ethylene oxide with raethylmagneeium bromide. In the years... 

Tertiary alky] Grignard reagents are extremely unreactive toward ethylene oxide, giving rise exclusively to ethylene haJohydrins under conditions normally suitable for reactions with primary or secondary Grignard reagents.898 s b jn other words, in terras of the... 

Condensation of Grignard reagents with alkyl-substituted ethylene oxides is fairly complex, particularly if the epoxides involved are asymmetric and massively substituted. The reaction course depends also on the structure of the Grignard reagent, and obviously on experimental conditions used for the condensation. 45 ... 

SAMPLE SOLUTION (a) Reaction with ethylene oxide results in the addition of a —CH2CH2OH unit to the Grignard reagent. The Grignard reagent derived from o-bromotoluene (or o-chlorotoluene or o-iodotoluene) is appropriate here. 

Our first task is to assemble 3-phenyl-1-propanol from the designated starting material benzyl alcohol. This requires formation of a primary alcohol with the original carbon chain extended by two carbons. The standard method for this transformation involves reaction of a Grignard reagent with ethylene oxide. 

The target molecule has four carbon atoms, suggesting a route involving reaction of an ethyl Grignard reagent with ethylene oxide. 

Reaction of the Grignard reagent with ethylene oxide, prepared in part (b), completes the synthesis. 

Hudrlik, P. F. Ahmed, M. E. Roberts, R. R. Hudrlik, A. M. Reactions of (triphenylsilyl) ethylene oxide with Grignard reagents (and with MgBr2). A reinvestigation./. Org. Chem. 1996, 61, 4395-4399. 

Write equations for the reaction of ethylene oxide or other epoxides with nucleophiles such as H+, and H20, H+ and alcohols, ora Grignard reagent. 

This process was superceded by the Friedel-Crafts reaction of benzene and ethylene oxide which is now the most important commercial process (11). Cheap ethylene oxide brought about this shift. For a short time, commercial quantities of phenylethyl alcohol were made by the Grignard reaction of phenyl magnesium chloride on ethylene oxide but this process could not compete with the Friedel-Crafts process. 

The first total synthesis of cinchonamine (277) and 2-epicinchonamine (278) proceeds via the epimers (279), which were prepared by two independent methods.169 Scheme 28 illustrates the more efficient of the two syntheses, which involves as its first stage the condensation of 2-lithio-iV-benzenesulphonyl-indole with N-benzoylmeroquinene aldehyde (280), itself obtained by reduction of the readily available JV-benzoylmeroquinene ester (281). The critical cyclization stage [(279)— (283)+ (284)] that occurs on prolonged heating at 155 °C presumably proceeds via the immonium ion (282), since separation of the epimers of (279) followed by dehydration and cyclization affords the same mixture of (283) and (284). Finally, the hydroxyethyl group was introduced by the reaction of the Grignard derivatives of (283) and (284) with ethylene oxide.169... 

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