Cyclopropyl ethers

The cyclopropanation of 1-trimethylsilyloxycyclohexene in the present procedure is accomplished by reaction with diiodomethane and diethylzinc in ethyl ether." This modification of the usual Simmons-Smith reaction in which diiodomethane and activated zinc are used has the advantage of being homogeneous and is often more effective for the cyclopropanation of olefins such as enol ethers which polymerize readily. However, in the case of trimethylsilyl enol ethers, the heterogeneous procedures with either zinc-copper couple or zinc-silver couple are also successful. Attempts by the checkers to carry out Part B in benzene or toluene at reflux instead of ethyl ether afforded the trimethylsilyl ether of 2-methylenecyclohexanol, evidently owing to zinc iodide-catalyzed isomerization of the initially formed cyclopropyl ether. The preparation of l-trimethylsilyloxybicyclo[4.1.0]heptane by cyclopropanation with diethylzinc and chloroiodomethane in the presence of oxygen has been reported. "... 

The isomerizatioA of 84S contrasts in a striking way with the response of bis-cyclopropyl ether 848 to electrophilic ring cleavage. In acidic methanol, cleavage of the cyclopropane ring toward oxygen results to give 849... 

Since the cyclopropanation reaction nsing zinc carbenoids is nsnally faster with electron-rich alkenes, it is not surprising to observe that enol ethers are nicely converted into cyclopropyl ethers in high yields (equation 17). ... 

A variety of geminally substituted cyclopropyl ethers are synthesized employing Fischer carbene complexes [(CO)5M=CR (OR2) M = Cr, Mo, W R1 = alkyl, alkenyl and aryl] as alkoxycarbene sources. Electron-deficient alkenes and conjugated dienes are suitable substrates for the reaction (equation 108)237-245. Electron-rich enol ethers and enamines are also... 

Cleavage of l-(trimethylsilyloxy)bicyclo[n.l.O]alkanes (8, 269-270). Lead tetraacetate fragmentation of the exo- and endo-methyl substituted silyl cyclopropyl ethers (1) is essentially stereospecific.2 Thus exo-1 is fragmented to the (E)-alke-noate 2 exclusively and endo-1 is converted into (Z)-2 exclusively. 

Enol ethers may also be cyclopropanated using zinc carbenoids stereoselectively. Furukawa cyclopropanation of enol ether 32 proceeds with high stereoselection, and the obtained cyclopropyl ether 33 can be easily transformed into the enantiomerically pure cyclopropyl alcohol 35 [30]. In this case, high stereoselectivity is achieved by employing the chiral diol 36, which is not commercially available. Using the commercially available enantiopure diol 37, the level of stereoselectivity is significantly lower (Scheme 7). 

In the irradiation of 3,10-dimethyl-3,5-hexalin (23) it has been found that five ethers are formed, the cyclopropyl ether (24) arising from the bicyclobutane and the ethers (25-28) coming from other intermediates. The amounts of these various products formed depend upon the concentration of methanol present during the irradiation. 

Before the reaction was started the air was displaced from the reaction system with argon. A solution of diphenyldiazomethane (10.5 g, 54 mmol) in freshly distilled butyl vinyl ether (50 mL) was then added drop-wise to a boiling solution of anhyd CuSO (0.3026 g, 1.90 mmol) in butyl vinyl ether (100 mL) with stirring for 4 h. When no more Nj was liberated (780 mL, 64.5yo), the mixture was cooled (in an atmosphere of argon) and the catalyst filtered off. Butyl vinyl ether was distilled off under vacuum and the resulting residue, after separation of benzophenone azine which had crystallized out, was fractionated under vacuum. A light-yellow distillate (11.1 g bp 133-155 C/0.2 Torr), which was a mixture of l-butoxy-2,2-diphenyl-cyclopropane (1), benzophenone azine (2) and benzophenone (3), was obtained. The cyclopropyl ether was isolated from this mixture by means of column chromatography (alumina activity II, hexane/EtjO 10 1) and was finally purified by vacuum distillation yield 2.36g (16%) bp 78 - 79°C/0.015 Torr. 

A large number of cyclopropanes containing a bond from oxygen to a cyclopropyl carbon atom have been synthesized from other cyclopropanes by substitution of a variety of substituents. The reagents utilized and the reaction conditions employed to achieve the transformations depend on the type of compound being prepared. The compounds can be divided into four groups cyclopropanols, cyclopropyl ethers, cyclopropyl esters, and oxaspiropentanes. 

If a carbene is generated under aqueous conditions or in the presence of an alcohol, e.g. by deamination of (V-nitroso-Ai -cyclopropylurea ° or thermal decomposition of 1-bromo-l-trimethylstannylcyclopropanes, cydopropanols or alkyl cyclopropyl ethers are inevitably formed, sometimes in fairly high yield, by solvent trapping of the carbene. This reaction, formally an intermolecular carbene insertion, is potentially a useful tool in mechanistic... 

Cyclopropanols afford alkyl cyclopropyl ethers on treatment with diazomethane, trial-kyloxonium tetrafluoroborate, tetrahydropyran, ethyl vinyl ether, or sodium hydride followed by iodomethane dimethyl sulfate has also been used. The yields are moderate to excellent. 

Alkyl cyclopropyl ethers, e.g. 5, have been prepared by treating the corresponding acetates with an alkyllithium (methyl- or butyllithium) and then with a methylating agent like ioodome-thane or trimethyloxonium tetrafluoroborate. ... 

Oxaspiropentanes are classified as a unique class of cyclopropyl ethers. Two reaction courses are recognized as being associated with the reaction in the presence of lithium bases. Treatment of oxaspiropentanes with butyllithium leads to S 2-type epoxy ring opening, giving butyl-connected cyclopropanols. On the other hand, with lithium amide as base there is deprotonation at the epoxy carbon followed by epoxide ring opening. The latter reaction offers a useful synthesis of 1-vinylcyclopropanols. ... 

The method has now been used to synthesize 9,10-dimethyl-trarcs-l-decalones,11 which have the characteristic C/D ring system of pentacyclic triterpenes. Thus i ruction of the hydroxy enol ether (9) with the Simmons-Smith reagent gives the cyclopropyl ether (10). Cleavage with 7% methanolic hydrochloric acid leads to the hydroxy ketone (11), convertible by Wolff-Kishner reduction followed by oxidation into (12). 

This reaction has been carried out on cyclopropanols these substances, however, are less available (2, 118-119) than trimethylsilyl cyclopropyl ethers and are readily decomposed by the hydrogen bromide formed on bromination. In the new synthesis, the by-product is trimethylbromosilane. 

P-Bromo ketones. 3-Bromo ketones (3) can be obtained in high yield by bromination of trimethylsilyl cyclopropyl ethers (2), prepared with the Simmons-Smith reagent from trimethylsilyl cnol ethers (1). ... 

Sugimura, T., Yashikawa, M., Futagawa, T., and Tai, A. (1990) Diastereo-differentiating cyclopropanation of a chiral enol ether a simple method for the preparation of optically pure cyclopropyl ethers. Tetrahedron 46,5955 - 5966. 

Cydopropanes, 18, 73-74 Cyclopropanols, 214-215 1-Cyclopropene-l-carboxylates, 296 Cydopropenyl ethers, 213, 214 Cydopropylcarbinyl bromides, 102 Cyclopropyl ethers, 213-214 Cyclopropyl ketones, 84 Cyclopropyl methyl ketone, 195 Cyclopropyl phenyl ketone. 195... 

Cyclopropyl ethers cyclopropeuyl ethers. Cyclopropyl ethers can be prepared in satisfactory yield by reaction of an alkene (excess) with chloromethyl ethers and LiTMP. The base eliminates HCl from the ether with formation of ROCH. 

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