The Preparation of α-Bromoacetals<sup>1</sup>

Marvell, Elliot N.; Joncich, M. J.

doi:10.1021/ja01147a025

Cited by 61 publications

(21 citation statements)

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“…Different types of acetals (13) have been oxidized by N-bromosuccinimide and no evidence has yet been obtained against a hydride transfer from the acetal to a bromonium ion as one of the key steps. Oxidation of acelal by hydride transfer with triethyloxonium tetrafluoroborate (14,15) and with triphenylmethane tetrafluoroborate (15) has also been described.…”

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The Oxidation of Acetals by Ozone

Deslongchamps¹,

Atlani²,

Frehel³

et al. 1974

Can. J. Chem.

140

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Ozone reacts very smoothly with acetals to give the corresponding esters. There are six gauche conformations that are theoretically possible for an acetal function. It is shown that only three of them are reactive toward ozone. It is proposed that a reactive acetal function must take a conformation in which each oxygen must have an electron pair orbital oriented antiperiplanar to the C—H bond. The mechanism of this reaction is also discussed.

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confidence: 99%

The Oxidation of Acetals by Ozone

Deslongchamps¹,

Atlani²,

Frehel³

et al. 1974

Can. J. Chem.

140

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“…The only one which does not follow this general course is the tetramethylated 1,3-dioxolane of experiment 1 1, and this goes to the other extreme in giving only the a,P-unsaturated, acetal. In contrast, the dehydrohalogenation of our dialkylacetals provides the a,P-unsaturated acetals, in some cases exclusively (experiments 13,16) and in other cases as the major product along with a smaller proportion (626%) of the ketene acetal (experiments 14,15,17).…”

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confidence: 83%

Base-catalyzed Dehydrobromination of Several α-Bromoacetals

Davis¹,

Brown²

1971

Can. J. Chem.

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Base-catalyzed dehydrohalogenation with potassium t-butoxide in t-butyl alcohol of the acetals obtained from homologues of a-bromoacetaldehyde and ethylene glycol[2-(a-bromoalky1)-l,3-dioxolanes] or 1,3-propanediol[2-(a-bromoalky1)-l,3-dioxane] provides the corresponding ketene acetal, in some cases exclusively and in others as the major product along with a smaller proportion of the a,b-unsaturated acetal. In contrast, similar dehydrohalogenation conditions convert the acetals obtained from homologues of a-bromoacetaldehyde and monohydroxy alcohols, to the a#-unsaturated acetals, in some cases exclusively, and in others as the major product accompanied by a smaller proportion of the corresponding ketene acetal.The preference for the ketene acetal formation from the 2-(a-bromoalky1)-l,3-dioxolanes (the ethylene acetals) is believed due to greater ease of approach by base to the methine proton as a result of the restricted shape of the 1,3-dioxolane ring. Approach by base to the methine proton of the a-bromoalkyl dialkylacetals is more hindered by the two alkoxy groups, which cause preferred attack by base at the proton to provide the a,a-unsaturated acetal.The proportion of a,a-unsaturated acetal obtained from base-catalyzed dehydrohalogenation of 2-(a-bromoalky1)-l,3-dioxolanes can be greatly increased if the reaction is carried out in dimethyl sulfoxide. This marked change in proportion of products is thought to be due to a change in mechanism occasioned by the dimethyl sulfoxide.La dChydrohalog6nation baso-catalys8e avec le t-butoxyde de potassium dam I'alcool t-butylique, La formation prkfkrentielle de IYac6tal ckt8ne a partir des (a-bromoalky1)-2 dioxolanes-1,3 (les BthyIkneac6tals) est probablement due a une plus grande facilite d'approche du proton methyne par la base et ceci probablement par suite de la forme restreinte du cycle du dioxolane-1,3. L'approche par une base du proton methyne des a-bromoalkyl dialkylac6tals est plus empikhk par les deux groupes alkoxy qui provoquent I'attaque preferentielle par une base sur le proton ! 3 pour conduire a un adtal a-a insatur6.Le proportion d'ac6tal a-!3 insaturC obtenu par d6hydrohalogenation baso-catalysk des (a-bromoa1kyl)-2 dioxolanes-1,3 peut &tre de beaucoup augmentee si la reaction est effectu6e dans le dimethyl sulfoxyde. Cette modification importante dam la proportion des produits obtenus est probablement due a un mecanisme different provoque par le dimethyl sulfoxyde. Canadian Journal of Chemistry, 49,2321 (1971)Introduction ketene acetals. They found that base-catalyzed For a part of our general study of the hydrogenolysis of acetals and ketals, several a,Punsaturated ethyleneacetals were required. The preparation of a few a,P-unsaturated dialkylacetals has been described by McElvain et al. dehydrohalogenatioi of a-haloacetals contaLing only hydrogen, aryl, or halogen substituents on the a carbon, gave only ketene acetals (1 in eq. a, Scheme 1). However, if the a carbon had attached to it a carbon atom bearing one or more hydrogen atoms, then only th...

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“…New reaction conditions (heating, solvent) for bromination by bromosuccinimide of diethylacetal enabled us to increase the yield of bromoacetaldehyde diethylacetal (Va) [5]. Variations of methods for preparing diethylacetal VI [6] (sequence of mixing reagents and excess of sodium) 1 increased the yield and purity of the final product.…”

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confidence: 99%