ChemInform Abstract: KONJUGIERTE HALOGENIERUNG UNGESAETTIGTER VERBINDUNGEN 5. MITT. KONJUGIERTE HALOGENIERUNG UNGESAETTIGTER VERBINDUNGEN IN GEGENWART VON ACETANHYDRID

Movsumzade, M. M.; Kyazimov, A. S.; Shabanov, A. L.; Alekperova, S.

doi:10.1002/chin.197222165

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“…By the brief contact with 95% sulfuric acid and n-pentane, 4-homobrend-3-ylcarbinol (4) was transformed predominantly into 4-homoisotwistane (15), while 2-methyl-4-homobrendan-2-ol (11) gave exclusively a mixture of 1-and 2-methyladamantane. 4-Homobrend-exo-and -endo-2-ylcarbinol (9x and 9n) afforded both 15 and methyladamantañes.…”

Section: Resultsmentioning

confidence: 99%

“…The first and last fractions contained small amounts of pure 13 and 14, respectively; IR and NMR spectra were identical with those of 13 and 14 already described in a separate procedure above. Upon preparative gas chromatographic separation, the center fraction afforded a pure sample of the previously reported" acetate 15 This mixture was washed with 25 mL of water. two 20-mL portions of 10% hydrochloric acid, and 25 mL of saturated sodium chloride solution; and then dried over magnesium sulfate.…”

Section: Discussionmentioning

confidence: 99%

“…Reaction of 2-Bromocyclohexanone (12) with LDA. Gas chromatographic and NMR analysis of the product from 667 mg of 2-bromocyclohexanone (2) indicated a 35:12:53 ratio of 2-bromocyclohex-l-enyl acetate (13) to 6-bromocyclohex-l-enyl acetate ( 14) to ci's-2-bromocyclohexyl acetate (15). Chromatography of this material on a silica gel column afforded a 50% total yield of product in three fractions.…”

Section: Methodsmentioning

confidence: 99%

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Reductions of .alpha.-substituted ketones by lithium diisopropylamide

Kowalski¹,

Creary²,

Rollin³

et al. 1978

J. Org. Chem.

108

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Certain enolizable a-halo-and a-methoxy-substituted ketones undergo rapid reaction with lithium diisopropylamide (LDA) to give reduction products via formal hydride transfer to the carbonyl in competition with enolizal tion. The reducing agent has been verified as LDA by isolation of the oxidized form, the isopropylimine of acetone. This nitrogen analogue of the Meerwein-Ponndorf-Verley reduction gives stereochemistry analogous to that of borohydride or lithium aluminum hydride reductions. From a synthetic standpoint the reduction process can be circumvented in favor of enolization by use of lithium tetramethylpiperidide or lithium hexamethyldisilazide. Reaction of LDA with nonenolizable ketones also leads to reduction, but this process stops short of completion. This has been interpreted in terms of competing nucleophilic addition of LDA to the carbonyl to give an adduct which reverts to starting ketone upon addition of water. Addition of a "ketone scavenger" (methyllithium) to the reaction mixture prior to water quenching does not eliminate the starting ketone. These experiments support the intervention of a 1.2-ketone-LDA adduct.Lithium diisopropylamide is widely used in synthesis as a hindered, nonnucleophilic base, effecting rapid, kinetically controlled enolization of ketones usually in high yield.2 During attempts to prepare enolate anions from a variety of enolizable a-halo and a-methoxy ketones by treatment with lithium diisopropylamide (LDA) we have found that, surprisingly, many of these substrates undergo reduction of the carbonyl group in competition with expected enolization. These reactions, over within minutes in ether or tetrahydrofuran (THF) solvent a t -78 "C, produce mixtures of reduction and enolization products in which for some ketones the former greatly predominates. Herein we describe the extent of such reduction for several types of ketones with varied a-substituents, the stereochemistry of the reduction, and the interactions of LDA with some nonenolizable ketones as well. Results and Discussion Reaction of a-Halo and a-Methoxy Ketones with LDA.We are aware of no reported cases in whi,ch LDA has caused reduction of an enolizable k e t~n e ;~ thus we were extremely surprised on examination of the products from the -78 OC reaction of phenacyl bromide 1 with LDA, followed by acetic 0 OAc OAc I 1. LDA.THF, -78 "c I 2. AC,O, -78 O c -PhC=CHBr + PhCHCH,Br 1 2 3anhydride. Obtained in 80% yield was a nearly 2:l mixture of two products, the minor one of which consisted of the anticipated enol acetate 2 (a single isomer as indicated by the NMR spectrum, b u t with stereochemistry yet t o be determined4).The major product proved to be bromo acetate 3, as shown by spectral comparison with authentic material5 prepared via acetylation of the sodium borohydride reduction product of 1. Thus, in the reaction of phenacyl bromide with LDA, reduction of the carbonyl group occurs almost twice as rapidly as ketone enolization. This type of reaction is not unique t o phenacyl bromide.Reaction of LDA with endo-...

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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