Reductive Cleavage of Benzannelated Cyclic Ethers and Amines: Synthetic Applications

Azzena, Ugo; Demartis, Salvatore; Pilo, Luciano; Piras, Elisabetta

doi:10.1016/s0040-4020(00)00783-3

Cited by 30 publications

(15 citation statements)

References 26 publications

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“…As already observed with phthalan (59), reductive metalation of symmetrical heterocycles (65, 67, 70) allows the generation of unsymmetrical organometallics as an approach to the synthesis of unsymmetrically disubstituted naphthalenes and biaryls [61][62][63]. Interestingly, reduction of 1,8-naphthalan (67) could lead to a single or a double reductive metalation reaction, depending upon the metal employed as a reducing agent.…”

Section: -Aryl-substituted and Benzocondensated Cyclic Ethersmentioning

confidence: 91%

“…The different reactivities evidenced in the lithium-and potassium-mediated reductive cleavages can be attributed to several factors, including different redox potentials of the metals and different leaving group abilities of lithium and potassium oxides. The results obtained in the reductive cleavage of lithium benzylic alcoholates (see below) suggest that the nature of the leaving group is important in determining the occurrence of a second reductive cleavage step [61,62].…”

Section: -Aryl-substituted and Benzocondensated Cyclic Ethersmentioning

confidence: 99%

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Benzylic Organometals via Reductive Metalation Procedures

Azzena¹,

Dettori²,

Pisano

2011

COC

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The review discusses two different reductive metalation approaches to the generation of benzylic organometals.In the first part, the scope of the generation of polar benzylic organometals by the reductive cleavage of carbon -heteroatom sigma bonds will be presented. Besides briefly showing the evolution of the technique, the review deals with recent achievements in the generation of benzylic derivatives of alkali metals by the reductive cleavage of carbon -halogen, carbon -oxygen, carbon -nitrogen and carbon -sulphur bonds. Significant synthetic applications of this procedure are described, showing that an appropriate choice of reaction conditions (solvent, temperature, alkali metal, employment of an electron shuttle) strongly affects the outcome of the cleavage reaction.In the second part, the application of the reductive metalation to carbon -carbon, carbon -oxygen and carbon -nitrogen double bonds is described, a procedure leading to the generation of vic-diorganometallic derivatives. Synthetic applications of these diorganometals are illustrated, underlining the possible application of 1,2-diarylsubstituted vic-dicarbanions as synthetic analogues of an activated form of an alkali metal that, however, function under homogeneous and mild reaction conditions.

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Section: -Aryl-substituted and Benzocondensated Cyclic Ethersmentioning

confidence: 91%

Section: -Aryl-substituted and Benzocondensated Cyclic Ethersmentioning

confidence: 99%

Benzylic Organometals via Reductive Metalation Procedures

Azzena¹,

Dettori²,

Pisano

2011

COC

Self Cite

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“…The corresponding magnesium derivatives participated in the same cyclization process (Scheme 2.31) [187]. [190], Y = S [191], Y = NMe [190]), and 243 (Y = O [190], Y = S [190,192], Y = NMe [190]), were all prepared through a benzylic carbon±heteroatom bond cleavage from the corresponding heterocycles by an arenecatalyzed lithiation and reacted with electrophiles to give polyfunctionalized molecules in a regioselective manner. In a similar way to phthalan 217 (Scheme 2.28), after the reaction with a first electrophile intermediates 242 (Y = S) [191] and 243 (Y = O) [192], underwent a second benzylic carbon±heteroatom bond cleavage to give a new organolithium compound, which reacted with a second electrophile, yielding polyfunctionalized biphenyls and naphthalenes, respectively after hydrolysis.…”

Section: Remote Allyl and Benzyllithium Compoundsmentioning

confidence: 99%

Polyfunctional Lithium Organometallics for Organic Synthesis

Yus¹,

Foubelo²

2005

Handbook of Functionalized Organometallics

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Multifunctional organic molecules can be achieved by reacting functionalized organolithium compounds [1] with electrophilic reagents, this fact makes these intermediates of relevant interest in synthetic organic chemistry [2]. Another remarkable fact concerning organolithium compounds, compared with other organometallic compounds is that they can be prepared following a great number of different methodologies [3]: hydrogen±lithium exchange (deprotonation), halogen±lithium exchange, transmetallation reactions, carbon±heteroatom bond cleavage and carbolithiation of multiple carbon±carbon bonds. However, the highly ionic character of the carbon±lithium bond [4] makes these compounds extremely reactive and also unstable, so the synthetic processes should be carried out in some cases under very mild reaction conditions.Regarding the stability of functionalized organolithium compounds, it depends mainly on three factors, the most important one being the compatibility of the functional group with the carbon±lithium bond, so in some cases the functionality should be protected. The hybridization of the carbon atom bonded to the lithium atom is also important, so sp derivatives are more stable than the corresponding sp 2 and these are more stable than the sp 3 ones as it happens to the corresponding carbanions. Finally, the relative position of the functionality and the carbanionic center is also relevant, probably the b-functionalized derivatives being the most unstable species due to the existence of two consecutive carbon atoms with opposite polarities, the b-elimination process to give an olefin is extremely favored. Stabilized organolithium compounds, such as lithium enolate intermediates [5], a-organolithium compounds bearing electron-withdrawing groups (RSO, RSO 2 , CN, NO 2 , etc.) and heteroatoms such as sulfur [6], selenium and phosphorus as well as functionalized aryllithium compounds will not be consider in depth in this chapter due to the limited length of this review.The following study is ordered based on the relative position of the functionality and the carbanionic center, as well as on the hybridization of that center.

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“…[17] PBr 3 (6.0 cm 3 , 0.064 mol) was added to a suspension of 1,8-bis(hydroxymethyl)naphthalene (3.93 g, 0.0209 mol) in dry dichloromethane (50 cm 3 ) under nitrogen. The resulting clear solution was stirred at room temperature for 5 h. After this period water was carefully added dropwise until the evolution of gas ceased.…”

Section: Preparation Of 18-bis(bromomethyl)naphthalenementioning

confidence: 99%

“…All analytical data match those previously published. [17] Preparation of 3-[(2-Methylthio)phenyl]pyrazole: This is a slight variant of the method published earlier. [5] A solution of 2Ј-(methylthio)acetophenone (4.28 g, 0.0257 mol) in dimethylformamidedimethylacetal (10 cm 3 , a large molar excess) was refluxed for 3 days under nitrogen to yield a dark brown solution.…”

Section: Preparation Of 18-bis(bromomethyl)naphthalenementioning

confidence: 99%

Mononuclear and Polynuclear Chain Complexes of a Series of Multinucleating N/S Donor Ligands

2005

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We have prepared a series of five ligands with potentially N,S‐bidentate chelating arms derived from 3‐[2‐(methylsulfanyl)phenyl]pyrazole linked to central aromatic spacers by methylene units. Complexes with a variety of architectures have been obtained, including simple mononuclear complexes and polynuclear chain complexes. The p‐xylyl‐spaced ligand L1 forms one‐dimensional helical coordination polymers with copper(I) and silver(I) ions. These polymers display interligand aromatic stacking interactions within each helical chain. The m‐xylyl‐spaced ligand L2 forms a coordination polymer with copper(I) but a mononuclear complex with the larger silver(I) ion in which the central phenyl ring is involved in an η1 π‐type Ag···C interaction with the AgI. The 3,3′‐biphenyl‐spaced ligand L3 also forms one‐dimensional polymers with silver(I) and copper(I) ions, but in this case the sequence of bridging ligands between one metal centre and the next follows a zig‐zag path rather than being helical. The 1,8‐naphthyl‐spaced ligand L4 only forms mononuclear complexes with copper(I) and silver(I) ions showing that this spacer is not large enough to enforce a bridging coordination mode. The three‐armed ligand L5, prepared from 2,4,6‐tris(bromomethyl)mesitylene, also forms a mononuclear complex with silver(I) ions, where one of the three arms is pendant. However, when excess silver(I) ions are present two of these mononuclear complexes can be assembled into the trinuclear complex [Ag3(L5)2](ClO4)3. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

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Reductive Cleavage of Benzannelated Cyclic Ethers and Amines: Synthetic Applications

Cited by 30 publications

References 26 publications

Benzylic Organometals via Reductive Metalation Procedures

Benzylic Organometals via Reductive Metalation Procedures

Polyfunctional Lithium Organometallics for Organic Synthesis

Mononuclear and Polynuclear Chain Complexes of a Series of Multinucleating N/S Donor Ligands

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