Mechanistic features of S N Ar reactions of neutral and cationic metal-complexed halogenobenzenes with methoxide

5,7-Dihydroxy-4-methylphthalide (lc). A solution of butyllithium (20 cm1 23, 1.5 M in hexane) was added under stirring to a solution of 3-acetyl-4-(l-(methoxyccarbonyl)ethyl]-2,5-dihydrofuran-2-one (2.1 g, 0.01 mol) in 50 cm3 5of dry THF at -70 °C. The mixture was left to stand at this temperature for 3 h and then was allowed to reach ambient temperature. The mixture was shaken with dilute hydrochloric acid and extracted with diethyl ether. The organic extract was evaporated to dryness.The residue was chromatographed over silica gel (70:30 hexane-Et^O) to give 0.45 g of 5,7-dihydroxy-4-methylphthalide (lc, 25% yield). Compound lc was identical with an authentic sample of 5,7-dihydroxy-4-methylphthalide:12 mp 240 °C; IR (Njuol) 3420, 3340,1720,1625 cm"1; NMR (CDC13) 6.4 (s, 1 H), 5.2 (s, 2 ), 2.05 (s, 3 H); MS, m/e 180 (49), 151 (100), 122 (33).thesis of 2-and 3-chlorophenyl methyl ethers from slightly activated 1,2-and 1,3-dichlorobenzene in the presence of 18-crown-6 in a PTC solid-liquid system has been also reported.6We have found that SNAr reactions of dichlorobenzenes with powerful nucleophiles such as thiolates can be much more easily performed under the conditions of liquidliquid PTC. Reactions were carried out, according to eq 1, by stirring at 110 °C under nitrogen a heterogeneous ci C. + RSH 3 (catalyst), KOH, H20 no"ec, n2 Acknowledgment. This work was supported by Progetto finalizzato Chimica fine e secondaria, CNR.

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“…Thiols, dichlorobenzenes, 3, and KOH were commercially available reagent grade products. The aqueous KOH- (6) Sam, D. J.; Simmons, . E. J.…”

Section: Methodsmentioning

confidence: 99%

Nucleophilic aromatic substitution reactions under phase-transfer conditions. Synthesis of alkyl aryl sulfides from isomeric dichlorobenzenes and thiolates

Landini¹,

Montanari²,

Rolla³

1983

J. Org. Chem.

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Organoiron and Organochromium Chemistry

Semmelhack

2001

Organometallics in Synthesis: A Manual

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Comparison of (η⁶‐Fluoroarene)tricarbonylchromium Complexes with Their Chloro‐analogs in Radical Aromatic Substitutions

2003

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Reactions of fluoroarene-Cr(CO)3 complexes with SmIz and carbonyl compounds in TB[F/HMPA at -40--60 4c afforded the corresponding radical aromatic substitution products in high yield. Compared to the corresponding chloroarene-Cr(CO)3 complexes, fluoroarene-Cr(CO)o complexes showed a higher effiaency and slightly lower regioselectivity . Keywords radical substitution, arenetricarbonylchromiium complexComplexation of an arene ring by a transition metal dramatically alters its electronic nature, resulting in the remarkable enhancement in reactivity of the arene ring toward nucleophilic addition. ' While nucleophilic addition to arene-metal complexes has been widely studied and utilized in organic synthesis, fewer works2-' have been reported on the radical addition to arene-metal complexes and the chemistry is far from being well established. Schmalz et al . first discovered the intramolecular ketyl or azaketyl radical addition and substitution reactions of methoxylated arene-Cr( CO 13 complexes to give the corresponding demethoxylated products. Merlic and co-workers tested the competition between intramolecular addition to a Cr( C0)3 complexed arene and intramolecualr addition to a non-complexes arene using PhCH(CD2I)Ph-Cr(C0)3 as the model and observed a 2 : 1 preference for radical addition to the non-complexed arene.3 In contrast, they estimated from competition experiments that intermolecular ketyl radical addition to benzenetricarbonylchmium is faster than that attack on benzene by a factor of at least 100, OOO . Later, we successfully carried out the intermolecular radical aromatic substitutions on chloroarene-Cr (CO 13 complexes by the reaction with SmI2 and carbonyl compounds.' To further explore the scope of the intermolecular radical substitutions, we here choose fluoroarene-Cr( C0)3 complexes to substitute for chloroarene-Cr ( CO)3 complexes in reactions with SmI2 and carbonyl compounds.Reaction of fluorobenzene-Cr( CO), (1) with acetone ( 2 equiv.) and SmI2 ( 4 equiv.) in THF/HMPA at -40--60 t underwent smoothly to afford the corresponding substitution product 2a in almost quantitative yield. Other ketones and even aldehydes showed similar behavior and the results are listed in Scheme 1. With ketones, excellent yields of substitution products 2 were achieved, while the yields with aldehydes were lowered. The reactions were very clean and no byproduct could be detected except that a small amount of starting material 1 was recovered in some cases. While dechlorination always occurred in some extent in the reaction of chlorobenzene-Cr( C O )~, ' there was no defluorination product observed in the reaction of 1. Compared with chlombenzene-Cr(CO)3, the fluom-analog 1 apparently showed a higher efficiency in the radical substitution reactions .'In order to gain more information on the reaction pattern of fluoroarene-Cr(C0)3 complexes, we chose 0 -, rnand p-fluomtoluene-Cr( CO)J ( o , m , p-3)' and complex 4* bearing an electron-withdrawing group as the model substrates and subjected them to the reactions wit...

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Mechanistic features of S N Ar reactions of neutral and cationic metal-complexed halogenobenzenes with methoxide

Cited by 21 publications

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Nucleophilic aromatic substitution reactions under phase-transfer conditions. Synthesis of alkyl aryl sulfides from isomeric dichlorobenzenes and thiolates

Nucleophilic aromatic substitution reactions under phase-transfer conditions. Synthesis of alkyl aryl sulfides from isomeric dichlorobenzenes and thiolates

Organoiron and Organochromium Chemistry

Comparison of (η⁶‐Fluoroarene)tricarbonylchromium Complexes with Their Chloro‐analogs in Radical Aromatic Substitutions

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Mechanistic features of S N Ar reactions of neutral and cationic metal-complexed halogenobenzenes with methoxide

Cited by 21 publications

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Nucleophilic aromatic substitution reactions under phase-transfer conditions. Synthesis of alkyl aryl sulfides from isomeric dichlorobenzenes and thiolates

Nucleophilic aromatic substitution reactions under phase-transfer conditions. Synthesis of alkyl aryl sulfides from isomeric dichlorobenzenes and thiolates

Organoiron and Organochromium Chemistry

Comparison of (η6‐Fluoroarene)tricarbonylchromium Complexes with Their Chloro‐analogs in Radical Aromatic Substitutions

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Comparison of (η⁶‐Fluoroarene)tricarbonylchromium Complexes with Their Chloro‐analogs in Radical Aromatic Substitutions