Regioselektive [4+3]-cycloadditionen von heterosubstituierten allylium-2-olaten (oxallylen) an 2-methylfuran

Föhlisch, Baldur; Flogaus, Robert; Oexle, Jutta; Schädel, Angelika

doi:10.1016/s0040-4039(01)90038-3

Cited by 21 publications

(5 citation statements)

References 5 publications

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“…[36] The solvolysis of the primary cycloadduct(s) cannot occur when the oxyallyl intermediate(s) are generated in lithium perchlorate/diethyl ether. [11,12] However, in this solvent the reaction between 30 and furan, in the presence of triethylamine, gave only a 23 % yield of the expected dichlorooxabicycles. Three of them could be isolated by MPLC (ratio of isomers ca.…”

Section: A 27a)mentioning

confidence: 97%

“…[1] The favored reaction path is cleavage of the C-1-C-3 bond of the halogenocyclopropanone, or rather its hemiacetal anion (8), with dissociative expulsion of a halide ion from the C-Hal bond. The α,β-unsaturated carboxylic acid esters are formed preferentially with the cis-configuration (11). [2] The same stereoselectivity was found for "classical" Favorskii rearrangements with bases in water where, e.g., 1,1,3-trihalogenobutan-2-ones 24 and 25, leading to 2,4-dihalogenated 8-oxabicyclo[3.2.1]oct-6-en-3-ones (26,27) as a mixture of endo-exo-stereoisomers.…”

Section: Introductionmentioning

confidence: 99%

“…sodium 2,2,2-trifluoroethoxide in trifluoroethanol (NaTFE/TFE). [11][12][13] Apart from 1,1,3-trichloroacetone, [12,14] to the best of our knowledge, the behavior of other acyclic trihalogeno ketones under conditions of trifluoroethanolysis has not been investigated.…”

Section: Introductionmentioning

confidence: 99%

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Base‐Induced Trifluoroethanolysis of Acyclic Di‐ and Trihalogeno Ketones: Favorskii Rearrangement and [4+3] Cycloaddition

Föhlisch¹,

Franz²,

Kreiselmeier³

2005

Eur J Org Chem

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Reactions of five acyclic dihalogeno‐ and trihalogeno ketones, representing the α,α‐, α,α′‐, α,α,α‐ and α,α,α′‐di‐ and trihalogeno substitution pattern, with sodium 2,2,2‐trifluoroethoxide in 2,2,2‐trifluoroethanol (NaTFE/TFE) in the presence of furan were investigated with the aim of obtaining [4+3] cycloadducts of the corresponding oxyallyl intermediates. Preference of Favorskii rearrangement over cycloaddition was observed with dichloromethyl isobutyl ketone (1a) and 1,3‐dibromobutan‐2‐one (12) that formed mainly the trifluoroethyl esters of 3‐chloro‐2‐isopropylpropanoic acid (9a), and (Z)‐but‐2‐enoic acid (isocrotonic acid) (13), respectively. 9a was dehydrohalogenated to form trifluoroethyl 3‐isopropylacrylate (11a). [4+3] Cycloaddition was favored with the 1,1,3‐trihalogenobutan‐2‐ones 24 and 25, leading to 2,4‐dihalogenated 8‐oxabicyclo[3.2.1]oct‐6‐en‐3‐ones (26, 27) as a mixture of endo‐exo‐stereoisomers. With trichloromethyl isobutyl ketone (30) the isomeric 2,4‐dichloro‐substituted oxabicycles (34) were formed in lithium perchlorate/diethyl ether/furan/triethylamine, while in NaTFE/TFE solvolytic displacement of one chloro substituent occurred, providing 2‐chloro‐4‐trifluoroethoxy‐4‐isopropyl‐8‐oxabicyclo[3.2.1]oct‐6‐en‐3‐one (36). By analogy, 27 reacted with sodium methoxide/methanol to form the methoxy‐substituted oxabicycles 39a and 39b. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

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Section: A 27a)mentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

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Base‐Induced Trifluoroethanolysis of Acyclic Di‐ and Trihalogeno Ketones: Favorskii Rearrangement and [4+3] Cycloaddition

Föhlisch¹,

Franz²,

Kreiselmeier³

2005

Eur J Org Chem

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“…[45] In the hope that regioselectivity and yield would be higher with the corresponding trichloro ketone 20 (Scheme 6) and sodium 2,2,2-trifluoroethoxide (NaTFE) in 2,2,2-trifluoroethanol (TFE), we investigated the reaction between 20 and furan 9. (Moreover, the trichloroketone 20 is easier to prepare on a multigram scale than the dichloromethyl analogue.…”

Section: Installation Of the Isopropyl Groupmentioning

confidence: 99%

Synthetic Approaches to Hydroazulenes and Guaianes through [4 + 3] Cycloadditions of Oxyallyl Intermediates

et al. 2006

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Building blocks for syntheses of guaiane and secoguaiane sesquiterpenoids were prepared by the title reaction. 4-(3-Methylfuran-2-yl)butan-2-one (1) was obtained in five steps from methyl 3-methylfuran-2-carboxylate (4), and treatment of 1 with pentachloroacetone and sodium 2,2,3,3-tetrafluoropropoxide in 2,2,3,3-tetrafluoropropan-1-ol produced a [4 + 3] cycloadduct that was dechlorinated without prior isolation to give the oxabicyclic diketone 2 in a low yield. A better route to diketone 2 was via the oxabicycle 10b, prepared in a high yield from 2-(but-3-en-1-yl)-3-methylfuran (9) and pentachloroacetone, followed by dechlorination. Treatment of 2 with dilute methanolic potassium hydroxide resulted in the cleavage of the oxa bridge, with formation of 3,8-dimethylazulen-4-ol (11). Catalytic hydrogenation of 2 afforded the saturated oxabicyclic diketone 14, intramolecu-

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“…However, both the endo selectivity and the regioselectivity have precedent. 6,7 We were interested in developing some new chemistry with the cycloadducts and chose to explore the quasi-Favorskii rearrangement. Recently, this reaction has been put to good use in synthesis by the groups of Kraus and Gambacorta.…”

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confidence: 99%

Dihalo-Substituted Cyclopentanones: Synthetic Equivalents of Cyclobutenes in Diels-Alder Reactions

Harmata¹,

Shao²

1999

Synthesis

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2,2-Dichlorocyclopentanone and 2,5-dibromocyclopentanone react with various dienes in the presence of base to afford cycloadducts derived from [4+3]cycloaddition of the corresponding cyclopentenyl oxyallylic cations. These cycloadducts are unstable but reduction with sodium borohydride affords alcohols which are stable and easily handled. Treatment of these alcohols with potassium hydride results in the formation of cyclobutane containing products. This transformation makes dihalogenated cyclopentanones synthetic equivalents of a variety of substituted cyclobutenes and allows easy access to Diels-Alder adducts of various cyclobutanes. Further, the initial [4+3] cycloadducts can be treated with carbon nucleophiles, and the resulting alkoxides also undergo the quasi-Favorskii reaction.The [4+3]-cycloaddition reaction of allylic cations with dienes in both its inter-and intramolecular manifestations represents a useful process for obtaining simple cyclic and polycyclic structures containing seven-membered rings. 1 As part of our continuing program involving the development and exploitation of this reaction, we report herein some recent studies involving the intermolecular cycloaddition reactions of simple cyclopentenyl oxyallylic cations.During the course of our work on the synthesis of cyclooctanoids via the intramolecular [4+3]-cycloaddition reaction of cyclopentenyl oxyallylic cations, 2 we observed the formation of certain halogenated side products. For example, treatment of 1 with LDA and triflyl chloride followed by stirring in 3M LiClO 4 in diethyl ether in the presence of triethylamine gave the cycloadducts 2a and 2b in 55% combined yield as a 16:1 mixture of isomers. Also formed in low yield was the chlorinated cycloadduct 3, which presumably arose from small amounts of dichlorination of 1. We became interested in the synthetic potential of such halogenated species and thus undertook a study of their synthesis and chemistry. Our initial studies have focused on intermolecular [4+3]-cycloaddition reactions of halogenated oxyallylic cations and quasi-Favorskii rearrangements of the cycloadducts.

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Regioselektive [4+3]-cycloadditionen von heterosubstituierten allylium-2-olaten (oxallylen) an 2-methylfuran

Cited by 21 publications

References 5 publications

Base‐Induced Trifluoroethanolysis of Acyclic Di‐ and Trihalogeno Ketones: Favorskii Rearrangement and [4+3] Cycloaddition

Base‐Induced Trifluoroethanolysis of Acyclic Di‐ and Trihalogeno Ketones: Favorskii Rearrangement and [4+3] Cycloaddition

Synthetic Approaches to Hydroazulenes and Guaianes through [4 + 3] Cycloadditions of Oxyallyl Intermediates

Dihalo-Substituted Cyclopentanones: Synthetic Equivalents of Cyclobutenes in Diels-Alder Reactions

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