The Ketene Acetals.

McElvain, S. M.

doi:10.1021/cr60142a003

Cited by 64 publications

(26 citation statements)

References 36 publications

(143 reference statements)

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“…Similar treatment of a-bromo-iso-valeraldehyde ethyleneacetal provided primarily the ketene acetal, but in this case the a,gunsaturated acetal was also formed, though only to the extent of 14% of the product (experiment 7, Table 1). These results are contrary to those expected on the basis of the previous work (1)(2)(3)(4). Accordingly, the dehydrohalogenation of several homologues of these a-bromoaldehyde ethyleneacetals (experiments 1, 2, 4, 8, 11) and of the acetal obtained from a-bromo-n-valeraldehyde and 1,3-propanediol (experiment 12) was investigated.…”

Section: Resultscontrasting

confidence: 69%

“…It is seen that base-catalyzed dehydrohalogenation of our 2-(a-bromoalky1)-l,3-dioxolanes (the ethyleneacetals) and of 2-(a-bromoalky1)-l,3-dioxane generally provides the ketene acetal in greater proportion, and in several cases exclusively (experiments [1][2][3][4]7,8,12). 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.…”

Section: Resultsmentioning

confidence: 99%

“…The residue when distilled gave 40 g (59%) of colorless liquid, b.p. 78-80" at 12 mm; qDZ3 1 The 60 MHz p.m.r. spectrum showed a doublet at .r 5.18 (IH, J -4 Hz for the methine proton); a multiplet centered at 6.1 (5H); and a doublet at 8.38 (3H, J -7 Hz).…”

Section: ( I I ) Preparation Of A-bromoacetalsmentioning

confidence: 99%

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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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Section: Resultscontrasting

confidence: 69%

Section: Resultsmentioning

confidence: 99%

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Base-catalyzed Dehydrobromination of Several α-Bromoacetals

Davis¹,

Brown²

1971

Can. J. Chem.

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“…Carbon blacksupported sulfuric acid catalysts with different acid strengths were prepared by the method described in an earlier publication. 13 Methylene chloride (Aldrich) was distilled over CaH 2 or KOH. THF (Aldrich) was distilled from Na/benzophenone just before use.…”

Section: Materials and Instrumentationmentioning

confidence: 99%

“…12, 13 Under various reaction conditions, both 1,2-vinyl addition and ring-opening polymerization are possible for five, six, and seven membered CKA monomers. 4,5 Usually 1,2-vinyl addition polymers are produced at low temperatures or ambient temperature in cationic polymerizations.…”

Section: Introductionmentioning

confidence: 99%