Mechanistic and synthetic aspects of intramolecular alkoxide–allene cyclizations

Magnus, Philip; Albaugh-Robertson, Pamela

doi:10.1039/c39840000804

Cited by 23 publications

(11 citation statements)

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“…Initial experiments were carried out using adamantanone, which was selected as a sterically crowded model ketone. As expected, slow addition of the ketone to in situ‐generated lithiated methoxyallene 9 in THF at −78 °C provided the corresponding allenyl alcohol 12 after aqueous workup as a single product in an excellent yield of 95 % 14b. Although this compound was stable in the solid state, it slowly converts into vinyloxirane 13 in a [D 6 ]acetone solution.…”

Section: Resultssupporting

confidence: 55%

“…The additions of 9 to aliphatic aldehydes and ketones typically lead to primary adducts ( 10 and 12 ) that can be cyclized under basic conditions or by Lewis acid catalysis to form 2,5‐dihydrofuran derivatives such as 11 (Scheme ) 14. However, in rare cases the competitive formation of the isomeric vinyloxiranes of type 13 as products of a 1,3‐cyclization was also noticed 14b…”

Section: Introductionmentioning

confidence: 99%

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Reactions of Cycloaliphatic Thioketones and Their Oxo Analogues with Lithiated Methoxyallene: A New Approach to Vinylthiiranes

Jasiński

Mlostoń

Stolarski

et al. 2014

Chemistry An Asian Journal

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Admantanethione smoothly reacted with lithiated methoxyallene at low temperatures yielding the expected allenyl-substituted thiolate, which upon aqueous work-up underwent spontaneous 1,3-cyclization to afford a hitherto unknown methoxy-substituted vinylthiirane derivative. The analogous reaction with adamantanone led to the corresponding allenyl alcohol that can be isolated and--depending on the conditions applied--either be converted into the corresponding vinyloxirane or into the 2,5-dihydrofuran derivative. Sterically more crowded thioketones were also combined with lithiated methoxyallene, but in these cases competitive 1,5-cyclization leading to isomeric dihydrothiophene derivatives was observed. DFT calculations of model intermediates and products show distinct energy differences of the sulfur and the corresponding oxygen compounds. Desulfurization of the adamantanethione-derived vinylthiirane yielded a methoxy-substituted 1,3-diene that was studied in cycloadditions with electron-deficient dienophiles. Whereas in the case of tetracyanoethylene the corresponding cyclobutane derivative was formed, the reaction with nitrosobenzene provided the expected 1,2-oxazine derivative. By reductive cleavage of the N-O bond this heterocycle was converted into an unsaturated amino alcohol bearing an adamantane moiety.

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Section: Resultssupporting

confidence: 55%

Section: Introductionmentioning

confidence: 99%

Reactions of Cycloaliphatic Thioketones and Their Oxo Analogues with Lithiated Methoxyallene: A New Approach to Vinylthiiranes

Jasiński

Mlostoń

Stolarski

et al. 2014

Chemistry An Asian Journal

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“…The exact mechanism of this seemingly simple cyclisation is still unclear in its details and an electron-transfer mechanism has been proposed by Magnus. 21 Despite this uncertainty this approach to dihydrofuran derivatives has been used in stereoselective synthesis, e.g. for the preparation of an enantiopure primarily helical compound 64 by repetitive additions of lithiated methoxyallene to carbonyl groups (Scheme 22).…”

Section: Deprotonation Of Alkoxyallenes and Reactions With Electrophilesmentioning

confidence: 99%

Alkoxyallenes as building blocks for organic synthesis

2014

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Alkoxyallenes are unusually versatile C3 building blocks in organic synthesis. Hence this tutorial review summarizes the most important transformations, including subsequent reactions and their applications in the synthesis of relevant compounds, e.g. natural products. The reactivity patterns involved and the synthons derived from alkoxyallenes are presented. Often alkoxyallenes can serve as substitutes of acrolein or acrolein acetals, utilisation of which has already led to interesting products. Most important is the use of lithiated alkoxyallenes which smoothly react with a variety of electrophiles and lead to products with unique substitution patterns. The heterocycles or carbocycles formed are intermediates for the stereoselective synthesis of natural products or for the preparation of other structurally relevant compounds. The different synthons being put into practice by the use of lithiated alkoxyallenes in these variations will be discussed.

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“…In a subsequent report, it has been suggested by Magnus et al that the reaction proceeds via a radical mechanism. 31 However, the method is limited to fairly simple substrates such as allenyl alcohol 3a, which was converted into dihydrofuran 4a as shown in Scheme 2 (transformation 1). Aryl-substituted allenyl alcohols like 3b as well as substrates bearing sensitive protecting groups, for example, compounds 3c and 3d, tend to undergo decomposition under the reaction conditions.…”

mentioning

confidence: 99%

“…Moreover, base-promoted isomerization processes may occur during the reaction, as exemplified by the cyclization of allenyl alcohol 3e to furan derivative 8 (Scheme 2, transformation 2), 32 and sterically demanding substrates such as adamantanone-derived adduct 3f may react to vinyl epoxide products like 9 (Scheme 2, transformation 3). 31 As part of our ongoing interest in alkoxyallene-derived 2,5-dihydrofurans 4 and 2,5-dihydropyrroles as useful intermediates in natural product synthesis, 1 we kept searching for more general reaction conditions for cyclization of the allenic precursors. As we have previously reported, many functionalized alkoxyallenyl alcohols 3 and alkoxyallenyl amines undergo cyclization with silver(I) salts in acetone or acetonitrile, 3 a protocol which is complementary to Brandsma's method.…”

mentioning

confidence: 99%

3-Alkoxy-2,5-dihydrofurans by Gold-Catalyzed Allenyl Cyclizations and Their Transformation into 1,4-Dicarbonyl Compounds, Cyclopentenones, and Butenolides

Brasholz¹,

Dugovic²,

Reißig³

2010

Synthesis

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The addition of lithiated alkoxyallenes to carbonyl compounds furnishes allenyl alcohols, which undergo a highly efficient and chemoselective 5-endo-trig cyclization to 3-alkoxy-2,5-dihydrofurans catalyzed by gold(I) chloride. The dihydrofurans produced can be either oxidized to b-alkoxy butenolides by a manganese(III) acetate catalyzed radical oxidation with tert-butyl hydroperoxide, or transformed into a,b-unsaturated g-keto aldehydes by an oxidative ring cleavage using DDQ in the presence of water. Treatment of the g-keto aldehydes with sodium methoxide in methanol promotes a diastereoselective intramolecular aldol addition furnishing alkoxy-substituted cyclopentenone derivatives in good yield.

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Mechanistic and synthetic aspects of intramolecular alkoxide–allene cyclizations

Cited by 23 publications

References 1 publication

Reactions of Cycloaliphatic Thioketones and Their Oxo Analogues with Lithiated Methoxyallene: A New Approach to Vinylthiiranes

Reactions of Cycloaliphatic Thioketones and Their Oxo Analogues with Lithiated Methoxyallene: A New Approach to Vinylthiiranes

Alkoxyallenes as building blocks for organic synthesis

3-Alkoxy-2,5-dihydrofurans by Gold-Catalyzed Allenyl Cyclizations and Their Transformation into 1,4-Dicarbonyl Compounds, Cyclopentenones, and Butenolides

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