Ketones, cyclopropyl methyl preparation

Good results are obtained by the oxidation of the commercially available cyclopropyl methyl ketone with sodium hypobromite solution, and the preparation may be regarded as an excellent example of the oxidation of the —COCH, group to —4COOH ... 

Commercial cyclopropyl methyl ketone (Matlieson Company) is redistilled through a Widmer column over 95 per cent, passes over at 110-8-111 -8°/757 mm. It is quite pure since it yields a semicarbazone, m.p. 117° the m.p. is unaffected by recrystallisation from aqueous alcohol. The ketone may be prepared from ethylene dibromide, ethyl acetoacetate and an excess of sodium ethoxide. 

In the examples given the preparative value depends upon the ready availability of the required methyl ketone thus pinacolone (Expt 5.98), cyclopropyl methyl ketone (Expt 7.1) and mesityl oxide (Expt 5.213) are converted into 2,2-dimeth-ylpropanoic acid, cyclopropanecarboxylic acid and 3,3-dimethylacrylic acid respectively (Expts 5.124 and 5.125). 

Methyl cyclopropyl ketone has been prepared from ethyl aceto-acetate and ethylene bromide,6 and by the action of methyl-magnesium bromide on cyclopropyl cyanide.6-7 The procedure described for its preparation from 5-chloro-2-pentanone is similar to that of Zelinsky and Dengin.8 5-Chloro-2-pentanone has been prepared by a number of methods.9 The procedure given is essentially that of Boon 10 and of Forman.11 A similar procedure has been used for the preparation of the corresponding bromo-and iodoketones.10... 

If the electron-withdrawing group is such that self-condensation does not occur then the anion can be generated in the normal manner. Thus, the anion 349 of cyclopropyl phenyl sulfone (348) can be readily prepared by treatment of the parent compound with n-butyllithium at 0°C in THF. The anion has been shown to condense in excellent yield with aldehydes, ketones, methyl iodide and allyl and benzyl bromides to yield 350. The... 

Methyl ketones are often directly prepared from carboxylic acids by reaction with methyllithium. Other simple alkyl ketones may also be prepared in the same fashion, making this a method that should be considered whenever these substrates are required. An important demonstration of this protocol was reported by Masamune and coworkers in their synthesis of chiral propionate surrogates (Scheme 13). The ethyl and cyclopropyl ketones are important starting materials for macrolide total synthesis and have been prepared on a large scale. The overall yield for the ethyl ketone is 65% using 3.5 equiv. of ethyllithium without protection of the hydroxy group. 

In a paper published along with that of Stevens and Wentland20 and in agreement with these authors, Keely and Tahk23 reported the independent synthesis of dl-mesembrine, also from I-methyl-3-(3,4-dimethoxyphenyl)-2-pyrroline and methyl vinyl ketone. In their work the cyclopropyl derivative 3b was prepared from the reaction of the anion of 3,4-dimethoxyphenylacetonitrile (lc) with ethylene dibromide in dimethyl sulfoxide and its sodium salt as solvent and base. Reduction with ethereal diisobutylaluminum hydride gave the aldehyde, which was condensed with excess methylamine in benzene-ether solution with calcium oxide as the dehydrating agent. 

An effort was made to prepare a butyl analogue containing a ring, but it was never completed. This was the cyclopropylmethyl isomer, 2,5-dimethoxy-4-cyclo-propylmethylamphetamine hydrochloride, DOCPM. Only the first step of its synthesis was complete (the reaction of cyclopropylcarboxylic acid chloride with p-dimethoxybenzene) and even it went badly. The desired ketone (2,5-dimethoxyphenyl cyclopropyl ketone) was most difficult to separate from the recovered starting ether. A promising approach would be the isolation of the phenol (2-hydroxy-5-methoxyphenyl cyclopropyl ketone) which is a beautiful yellow solid with a melting point of 99-100 °C from methanol. Anal. (Cl 1 HI203) C,H. It then could be methylated to the wanted intermediate. It is the major product when the reaction is conducted with anhydrous aluminum chloride in methylene chloride. 

This reaction was first reported by Nenitzescu in 1931. It is the formation of an a,p-unsaturated ketone directly by aluminum chloride-promoted acylation of alkenes with acyl halides. Therefore, it is known as the Darzens-Nenitzescu reaction (or Nenitzescu reductive acylation), or Nenitzescu acylation. Under such reaction conditions, Nenitzescu prepared 2-butenyl methyl ketone from acetyl chloride and 1-butene and dimethylacetylcyclohex-ene from acetyl chloride and cyclooctene. However, in the presence of benzene or hexane, the saturated ketones are often resolved, as supported by the preparation of 4-phenyl cyclohexyl methyl ketone from the reaction of cyclohexene and acetyl chloride in benzene, and the synthesis of 3- or 4-methylcyclohexyl methyl ketone by refluxing the mixture of cycloheptene and acetyl chloride in cyclohexane or isopentane. This is probably caused by the intermolecular hydrogen transfer from the solvent. In addition, owing to its intrinsic strain, cyclopropyl group reacts in a manner similar to an oleflnic functionality so that it can be readily acylated. It should be pointed out that under various reaction conditions, the Darzens-Nenitzescu reaction is often complicated by the formation of -halo ketones, 3,)/-enones, or /3-acyloxy ketones. This complication can be overcome by an aluminum chloride-promoted acylation with vinyl mercuric chloride, resulting in a high purity of stereochemistry. ... 

A project directed towards the synthesis of chrysanthemic acid enantiomers illustrates some of our recent work on cyclopropano-pyranosides. The sequence (Scheme 40) that had worked so well (25) for the preparation of the simple cyclopropyl ketone (169) from the methanol adduct (168) was not adaptable for preparation of the gem-dimethyl analogue (171). The photoaddition of isopropanol to (83) gave an excellent yield of (170), but efforts to convert this into (171) were not encouraging. However, the Wittig cyclopropanation (24) of epoxide (51) gave the ester (172) whose stereochemistry was deduced by two pieces of nmr data (a) the value J12 < 1 Hz (76) (see Scheme 4), and (b) a ten percent Nuclear Overhauser Effect between H-1 and the methyl protons. 

Modhephene, 34, was the first isolated propellane natural product. As such, the Weiss-Cook reaction was the perfect method for its construction. The process began with the condensation of 2 with diketone 27. Standard conditions for decarboxylation produced the core scaffold 28. Hydrogenation of the mono-enol phosphate afforded the monoketone 29. The cyclopropyl derivative 30 was prepared by copper-catalyzed decomposition of a diazoketone. gem-Dimethylation to generate 31 preceded carboxylation and esterification to afford the advanced intermediate 32. Cuprate-induced cyclopropane ring opening and methylation of the 3-ketoester introduced the final carbon atoms giving rise to 33. Lithium iodide induced decarboxylation preceded reduction of the ketone followed by dehydration with Martin s sulfurane, thus producing 34. 

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