Samarium(II)-Promoted Radical Spirocyclization onto an Aromatic Ring

Ohno, Hiroaki; Okumura, Mitsutaka; Maeda, Shinichiro; Iwasaki, H.; Wakayama, Ryutaro; Tanaka, Tetsuaki

doi:10.1021/jo034767w

Cited by 56 publications

(28 citation statements)

References 45 publications

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“…[26,27] As an additional crucial feature the stabilities of the resulting cyclohexadienyl radicals C have to be considered and the reduction of C to cyclohexadienyl anions D is also important. [28] In accordance with literature precedent [25] we suggest that formation of B and of C are reversible processes and that the second electron transfer yielding D is the reaction determining step. For cyano-, acetyl-, and alkoxycarbonyl-substituted precur- …”

Section: Discussionsupporting

confidence: 88%

“…The conversion of 33 and related methoxycarbonyl-substituted aryl ketones with samarium diiodide into spiro compounds has been thoroughly investigated by Tanaka and co-workers. [25] They generally used five equivalents of samarium diiodide and hence compound 34 was obtained only as minor product. Under their conditions the electron-deficient double bond of 34 was further reduced to provide the major product with a cyclohexene moiety.…”

Section: γ-Aryl Ketones With O-substituentsmentioning

confidence: 99%

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Samarium Diiodide Mediated Ketyl–Aryl Coupling Reactions – Influence of Substituents and Trapping Experiments

Wefelscheid¹,

Berndt²,

Reißig³

2008

Eur J Org Chem

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This comprehensive study describes the influence of substituents at the aryl moiety on SmI 2 -mediated intramolecular ketyl-aryl coupling reactions. Differently substituted γ-aryl ketones were employed as precursors, which were directly prepared by Heck reactions of 4-penten-2-ol with the corresponding bromo-or iodobenzenes. After treatment with two equivalents of samarium diiodide γ-aryl ketones bearing electron-withdrawing substituents such as cyano, trifluoromethyl or carbonyl groups gave the expected hexahydronaphthalene derivatives as single diastereoisomers in most cases. The position of the substituents was also of crucial influence on the outcome; in several cases ipso-substitution leading to the formation of spiro compounds was observed. Electron-donating substituents at the aromatic moi-

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Section: Discussionsupporting

confidence: 88%

Section: γ-Aryl Ketones With O-substituentsmentioning

confidence: 99%

Samarium Diiodide Mediated Ketyl–Aryl Coupling Reactions – Influence of Substituents and Trapping Experiments

Wefelscheid¹,

Berndt²,

Reißig³

2008

Eur J Org Chem

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“…[27,28] The finding that the copper catalyst appears to be intimately involved in the transformation of 4 into 6 leads us to suggest that the reaction proceeds via the spirocyclic lactone 20, the product of a 4-exo radical cyclization onto the aromatic ring. [29] Once spirocyclization has taken place, presumably via the intermediacy of radical 19, we envisage that lactone 20 suffers a rapid loss of CO 2 to produce the vinyl chloride 21.…”

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confidence: 99%

A Remarkably Simple and Efficient Benzannulation Reaction

2007

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Dedicated to Professor E. J. Thomas on the occasion of his 60th BirthdayWhereas the application of atom-transfer radical cyclization reactions [1] (ATRC reactions) to the synthesis of g-butyrolactams and g-butyrolactones is now reasonably well established, [2] the same cannot be said of this approach to the synthesis of medium-sized rings.[3] Previously [4d] we had shown that the trichloroacetate 1 (Scheme 1) undergoes sequential 5-exo, 6-exo ATRC reactions to provide rapid access to the 2-oxabicyclo[4.3.0]nonane ring system. Alternate modes of cyclization (by 9-exo or 10-endo pathways [5] ) were not observed. As a continuation of our interest [4] in this area we investigated the cyclization of trichloroacetate 3 (Scheme 1) under ATRC conditions. The synthesis of benzoxocins by radical cyclization reactions has received scant attention, [6,7] and at the outset we wished to determine if ATRC of 3 would occur by a 7-exo or 8-endo pathway [8] and whether structural features could be incorporated into the substrate to modify the regiochemical outcome of the reaction.[9] Furthermore, we also believed that this potentially problematic cyclization [10] reaction would also serve as a suitable test case for the development and evaluation of more efficient catalysts for ATRC reactions. [11] Cyclization (CuCl, 5 mol %; 2, [12,13] 5 mol %; toluene; reflux) of the readily available ester 3 proved to be rather sluggish (95 % completion after 48 h) and afforded the labile [13] lactone 4 through an 8-endo-trig reaction. [7] This cyclization was also accompanied by the formation of a minor, wholly aromatic, by-product whose generation lagged behind the formation of lactone 4. Repeating the ATRC reaction of 3 for 120 h in refluxing toluene resulted in the total consumption of both ester 3 and the lactone 4, and the formation of 1-chloronaphthalene (6), which was isolated [14] in 23 % yield after column chromatography. Moreover we were delighted to observe that irradiation [15][16][17] of a solution of the ester 3 in 1,2-dichloroethane containing our standard catalyst system in a microwave reactor [18] afforded 6 in 84 % yield after a much reduced reaction time of two hours (Scheme 1).Wishing to establish the synthetic generality of this reaction, we subjected a variety of readily available aryl trichloroacetates (8, 10, 12 a-12 f; Scheme 2) to the same experimental protocol and found that, in each case, benzannulation proceeded smoothly over two hours at 200 8C to produce their respective naphthalene derivatives. The requisite ortho-allyl phenols used in this study are themselves readily available from an ortho-Claisen rearrangement [19] of their respective allyl aryl ethers, a process which in many cases can also be efficiently accomplished in a microwave reactor. [20] Of note is the observation that the benzannulation reaction proceeds with complete regiochemical control to afford an aryl chloride as a single regioisomer in each case. For example, subjecting the isomeric naphthyl esters 8 and 10 separately to our standard react...

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“…Although space restriction does not permit a detailed description, our group developed some other interesting novel reactions such as (1) stereoselective synthesis of 1,3-amino alcohols via allenylindium reagents using 2-ethynylaziridines as chiral carbon nucleophiles, 143,144) (2) samarium(II)-mediated radical cyclization onto an aromatic group, [174][175][176][177][178] (3) synthesis and isomerization of vinylaziridines and their application to the stereoselective synthesis of (E)-alkene dipeptide isosteres. [64][65][66][67]179,180) The author hopes the presented reactions based on the novel reactivities of allenes will facilitate further development of allene chemistry [181][182][183] and application to synthesis of pharmacologically important compounds from this class of compounds.…”

Section: Resultsmentioning

confidence: 99%

Samarium(II)-Promoted Radical Spirocyclization onto an Aromatic Ring

Cited by 56 publications

References 45 publications

Samarium Diiodide Mediated Ketyl–Aryl Coupling Reactions – Influence of Substituents and Trapping Experiments

Samarium Diiodide Mediated Ketyl–Aryl Coupling Reactions – Influence of Substituents and Trapping Experiments

A Remarkably Simple and Efficient Benzannulation Reaction

Development of Useful Reactions Involving Tandem Cyclizations Based on the Novel Reactivities of Allenic Compounds

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