HYDROGENOLYSIS BY AlCl3–LiAlH4 OF ETHER SOLUTIONS OF cis AND trans ISOMERS OF 2,4-DISUBSTITUTED-1,3-DIOXOLANES

Leggetter, B. E.; Brown, R. K.

doi:10.1139/v65-140

Cited by 19 publications

(4 citation statements)

References 7 publications

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“…Few free-energy differences between diastereoisomeric five-membered ring systems have been measured with precision. [29][30][31][32][33] Recent equilibration studies, used in conjunction with nmr spectroscopy, proved to be a powerful tool in the conformational analysis of substituted 1,3-dioxanes. 34 It was hoped that the same type of study, applied to the 1,3-dioxolane system, would lead to a better understanding of the conformation of fivemembered rings in general.…”

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confidence: 99%

Conformational analysis. XXIII. 1,3-Dioxolanes

Willy¹,

Binsch²,

Eliel³

1970

J. Am. Chem. Soc.

131

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Two series, one of 2,4-di-and one of 2,r-4,m-5-trialkyl-substituted 1,3-dioxolanes, have been studied through acid-catalyzed equilibration of diastereoisomers and by nuclear magnetic resonance spectroscopy. Freeenergy differences between diastereoisomers are small, and nearly constant within each series spanning the ranges 0.3-0.5 kcal/mol for the dialkyl series and 0.2-0.7 kcal/mol for the trialkyl series in favor of the cis-2 or syn-2 substituents.Exceptions are 2-í-butyl-r-4,c¡'j-5-diisopropyl-l,3-dioxolane (+0.22 kcal/mol), 2-isopropyl-r-4,m-5di-?-butyl-l ,3-dioxolane (+0.01 kcal/mol), and the corresponding 2-i-butyl homolog (+0.92 kcal/mol) (in favor of the anti isomer). The data suggest a highly flexible five-membered ring with only the most bulky substituents showing signs of specific steric interactions. onformational analysis3 of five-membered ring systems, although of considerable interest because of the widespread occurrence of such systems in nature (e.g., in carbohydrates, steroids, alkaloids, nucleic acids, and certain amino acids), has progressed much more slowly than the corresponding analysis of the sixmembered homologs, largely due to the complications caused by the conformational mobility of five-membered rings.4-9 Until recently it had been considered that "envelope" (1) or "half-chair" (2) forms8•10•11 were adequate models for a description of the conformation of a given fivemembered ring system since these two forms were postulated as the most stable forms in much of the pioneering work on five-membered rings (cyclopentane and its derivatives).4-14 In subsequent work on 1,3dioxolanes, it was similarly assumed, a priori, that one or the other of the two forms should be the thermodynamically most stable.

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confidence: 99%

Conformational analysis. XXIII. 1,3-Dioxolanes

Willy¹,

Binsch²,

Eliel³

1970

J. Am. Chem. Soc.

131

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“…Electron donor substituents (R = methyl or phenyl in Scheme I) attached to C-2 accelerate the cleavage by stabilization of the transition state leading to the formation of the intermediate oxocarbonium ion, the step which is considered to be rate determining (1)(2)(3)(4), whereas electron-withdrawing groups (chloromethyl, dichloromethyl) attached to C-2 retard the reductive cleavage.…”

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The Influence of Heteroatom-substituted Methyl Groups and of Vinyl Groups (CR₂=CR—) Attached to C-2 of 1,3-Dioxolanes on the Ease and Direction of Hydrogenolysis of the 1,3-Dioxolanes by AlH₂Cl, AlH₃, or LiAlH₄

Davis¹,

Brown²

1971

Can. J. Chem.

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Heteroatom substituents on the methyl group of 2-methyl-1,3-dioxolane retard the rate of hydrogenolysis by AIHzCl of ether solutions of the z-substituted 1,3-dioxolanes. The effectiveness of the heteroatoms in decreasing the ease of hydrogenolysis is H < S < 0 < Br < NR,. This retardation is thought to be due to the destabilization of the transition state leading to the intermediate oxocarboniurn ion, caused by the electronegativity of the heteroatom and/or coordination of some of the AIHzCl with the heteroatom.AIHzCl or AlH, in diethyl ether at room temperature reduces 2-vinyl-or 2-[alkyl (or aryl) substituted vinyl]-1,3-dioxolanes to only the P,y-unsaturated alkyl P-hydroxyethyl ether, the product expected from hydride ion addition to C-2 of the 1,3-dioxolane. The ease of hydrogenolysis increases with increasing alkyl (or aryl) substitution on the 2-vinyl group.LiAlH, in diethyl ether at room temperature, or in di-n-propyl ether or 1,2-dimethoxyethane @ME) at room temperature or reflux temperature, reduces 2-vinyl-1,3-dioxolane only to a-propenyl P-hydroxyethyl ether. This product is the result of hydride addition to the P-carbon of the vinyl group accompanied by ring opening and double bond migration. Alkyl substituents attached to the vinyl group of 2-vinyl-1,3-dioxolane markedly retard the rate of hydrogenolysis by LiAIH4 in the dialkyl ethers at room temperature, but at the reflux temperature (90") of di-n-propyl ether the 2-alkylated vinyl-1,3-dioxolanes are hydrogenolyzed, but only to the P,y-unsaturated alkyl P-hydroxyethyl ether. In refluxing DME (80") the 2-alkylated vinyl-l,3-dioxolanes give primarily, if not exclusively, the a,P-unsaturated alkyl P-hydroxyethyl ether. A rationale is suggested to account for these results.LiAlH4 in diethyl ether reduces 2-styryl-1,3-dioxolane only to f3-phenylethyl-1,3-dioxolane, by hydride addition to the olehic carbon P to the phenyl group.Les substituants heteroatomiques situes sur le groupe rnethyle du methyl-2 dioxolane-1,3 ralentissent la vitesse d'hydrogbnolyse par AIHzCl des solutions etherbes des dioxolanes-1,3 substitues en 2. L'efficacite des heteroatomes dans la diminution de la facilite d'hydrogenolyse est H < S < 0 < Br < NR,.On pense que ce ralentissement est du a la destabilisation de l'etat de transition qui conduit a I'ion oxocarbonium intermediaire a cause de l'electronegativite de l'heteroatorne et/ou de la coordination d'une certaine quantite de AIHzCl avec l'het6roatorne.AIHzCl ou AlH3 dans 1'6ther diethylique reduit quantitativement a la temperature ordinaire les vinyl-2 ou les vinyl-2 [substituks par un-groupe,alkyle'(ou aryle)] dioxolanes-1,3 en alkyl p,y-insature 0-hydroxyethyl Bther qui est le produit attendu lors de I'addition d'un ion hydrure sur le C-2 d'un dioxolane-1,3. La facilite de I'hydrogknolyse croit avec I'augmentation de la substitution par un groupe alkyle (ou aryle) sur le groupe vinyle en position 2.LiAIH4 dans 1'6ther diethylique la temperature ordinaire, ou dans Ether di-n-propylique ou dans le dimkthoxy-1,2 ethane (DME) L...

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“…The complete conversion of benzaldehyde to oxolanes (1,2), the reaction of A1H2C1 with 1 benzyl alcohol by 3 in less than 1 h shows that the first involves formation of a complex 2 due to the single hydride unit in 3 is available for reduction Lewis acidity of AlH2Cl, and this complex subse-of carbonyl compounds and it is not the bulk of quently forms an alkoxyhydridoaluminum chlor-reagent 3 which causes its failure to react with 1. ide 3 (Scheme I).…”

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“…Canadian Journal of Chemistry, 49, 2168 (1971) Xenon difluoride was recently found to be a useful reagent for aromatic substitution reactions in the liquid phase, in the presence of hydrogen fluoride as catalyst (I), as well as in the vapor phase at temperatures 100-200" (2).…”

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The Number of Hydride Ions in AlH₂Cl Available for Hydrogenolysis of 1,3-Dioxolanes

Davis¹,

Brown²

1971

Can. J. Chem.

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2-Methyl-l,3-dioxolane (1) in ether is hydrogenolyzed completely to 2-ethoxyethanol by an equimolar proportion of AIH,CI, whereas a 112 mol of AIH2CI hydrogenolyzes 1 mol of 1 only to the extent of 50%. In the latter case, the intermediate compound 2-ethoxyethoxyhydridoaluminum chloride (CzHSOCH2-CH20AIHCI) formed with half of the 2-methyl-1,3-dioxolane, even though it contains a hydride ion, fails to react with the remainder of the dioxolane. This is believed due to the preference of C,HsOCH2-CH20AIHCI to form an internal Lewis acid-base complex rather than form a similar complex with 1, a step essential to facilitate the hydrogenolysis of 1.La reaction dans I'kther entre le mkthyl-2 dioxolane-1,3 (1) et une proportion molaue de AlH,CI conduit ti I'kthoxy-2 kthanol provenant d'une hydrogknolyse complete; par ailleurs I'action d'une demimole de AlH2Cl sur une mole de 1 conduit ti une hydrogknolyse de 50% de ce composk. Dans ce cas, le composk intermkdiaire (C2HsOCH2CH20AIHC1) fomk avec la moitiC du dioxolane 1 contient encore un ion hydrure mais il ne rkagit toutefois pas avec le restant du dioxolane. On croit que ce phknomene est du ti la prkfkrence de I'intermkdiaire ti former un complexe de Lewis interne plut6t que de former avec 1 un complexe semblable qui est essentiel pour faciliter I'hydrogknolyse de 1.Canadian Journal of Chemistry, 49. 2166Chemistry, 49. (1971 In connection with a study of the LiAlH,-of epoxides by the mixed hydride (3, 4) and AlCl, (mixed hydride) reductive cleavage of alkoxyaluminum hydrides have been prepared 1,3-dioxolanes in this laboratory, we have found and used to hydrogenolyze epoxides (5), it apthat 2-methyl-l,3-dioxolane (1, Scheme 1) is con-pears from our work that 3 cannot hydrogenolyze verted completely to 2-ethoxyethanol 4 in less 1. That this is so has been shown by the failure to than 30 min by an equimolar proportion of di-observe any reductive cleavage when an ether hydridoaluminum chloride, AlH2C1.2 However, solution of 1 was treated for as long as 48 h with no more than 50% conversion of 1 to 4 could be 3, prepared separately by the reaction of A1H2C1 obtained if a h a y molar proportion of AlH2C1 with an equimolar amount of 2-ethoxyethanol was used, even if the reaction time was extended according to directions (5) which describe the to 48 h. In accordance with the views concerning preparation of alkoxyaluminum hydrides. the course of the reductive cleavage of 1,3-di-The complete conversion of benzaldehyde to oxolanes (1, 2), the reaction of A1H2C1 with 1 benzyl alcohol by 3 in less than 1 h shows that the first involves formation of a complex 2 due to the single hydride unit in 3 is available for reduction Lewis acidity of AlH2Cl, and this complex subse-of carbonyl compounds and it is not the bulk of quently forms an alkoxyhydridoaluminum chlor-reagent 3 which causes its failure to react with 1. ide 3 (Scheme I).Furthermore, we have also shown that 1 is conAlthough alkoxyaluminum hydrides have been verted to 2-ethoxyethanol 4 in less than 30 min postulated as int...

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HYDROGENOLYSIS BY AlCl₃–LiAlH₄ OF ETHER SOLUTIONS OF cis AND trans ISOMERS OF 2,4-DISUBSTITUTED-1,3-DIOXOLANES

Cited by 19 publications

References 7 publications

Conformational analysis. XXIII. 1,3-Dioxolanes

Conformational analysis. XXIII. 1,3-Dioxolanes

The Influence of Heteroatom-substituted Methyl Groups and of Vinyl Groups (CR₂=CR—) Attached to C-2 of 1,3-Dioxolanes on the Ease and Direction of Hydrogenolysis of the 1,3-Dioxolanes by AlH₂Cl, AlH₃, or LiAlH₄

The Number of Hydride Ions in AlH₂Cl Available for Hydrogenolysis of 1,3-Dioxolanes

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HYDROGENOLYSIS BY AlCl3–LiAlH4 OF ETHER SOLUTIONS OF cis AND trans ISOMERS OF 2,4-DISUBSTITUTED-1,3-DIOXOLANES

Cited by 19 publications

References 7 publications

Conformational analysis. XXIII. 1,3-Dioxolanes

Conformational analysis. XXIII. 1,3-Dioxolanes

The Influence of Heteroatom-substituted Methyl Groups and of Vinyl Groups (CR2=CR—) Attached to C-2 of 1,3-Dioxolanes on the Ease and Direction of Hydrogenolysis of the 1,3-Dioxolanes by AlH2Cl, AlH3, or LiAlH4

The Number of Hydride Ions in AlH2Cl Available for Hydrogenolysis of 1,3-Dioxolanes

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HYDROGENOLYSIS BY AlCl₃–LiAlH₄ OF ETHER SOLUTIONS OF cis AND trans ISOMERS OF 2,4-DISUBSTITUTED-1,3-DIOXOLANES

The Influence of Heteroatom-substituted Methyl Groups and of Vinyl Groups (CR₂=CR—) Attached to C-2 of 1,3-Dioxolanes on the Ease and Direction of Hydrogenolysis of the 1,3-Dioxolanes by AlH₂Cl, AlH₃, or LiAlH₄

The Number of Hydride Ions in AlH₂Cl Available for Hydrogenolysis of 1,3-Dioxolanes