Zinc- and Indium-Mediated Ring-Expansion Reaction of α-Halomethyl Cyclic β-Keto Esters in Aqueous Alcohol

Sugi, Masaaki; Sakuma, Daisuke; Togo, Hideo

doi:10.1021/jo030092l

Cited by 37 publications

(16 citation statements)

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“…EtO 2 CCHN 2 ), known to insert regioselectively at the least-substituted carbon alpha to ketones, using BF 3 ·Et 2 O [26] or Meerwein's salt [27] failed, as did non-stabilized carbenoids, [28] ethyl diazolithioacetate [29] and silyloxycyclopropane homologation. [30] Considering BeckwithDowd [31] and variant [32] ring expansion protocols are widely reported, 26 was converted, using Mander's reagent [33] and subsequent retro Dieckmann/Dieckmann reaction, to 36 (X-ray crystal structure of α-CO 2 Et, see Figure 4) in 69 % overall yield. All attempts to convert 36 to the methylene iodide 37 or bromide 38 failed when 36 was reacted directly with diiodo-or dibromomethane.…”

Section: Introductionmentioning

confidence: 99%

“…Reaction of 36 with formalin [34] gave the methylene hydroxy derivative 39 (84 %), which using triphenylphosphane iodine and imidazole gave iodide 37 (75 %). Unfortunately, treating iodide 37 with sa- marium diiodide [35] only afforded cyclopropanol 40 (72 %) and unidentified products, whereas zinc metal [36] only returned starting material (Scheme 8). Attempts (e.g.…”

Section: Introductionmentioning

confidence: 99%

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Towards the Total Synthesis of Vibsanin E, 15‐O‐Methylcyclovibsanin B,3‐Hydroxyvibsanin E, Furanovibsanin A, and 3‐O‐Methylfuranovibsanin A

et al. 2006

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Studies detailing synthetic approaches to a variety of biosynthetically related vibsanin‐type diterpenes (i.e. vibsanin E, 15‐O‐methylcyclovibsanin B, 3‐hydroxy‐vibsanin E, furanovibsanin A, and 3‐O‐methylfuranovibsanin A) are discussed. Biogenetically modelled approaches are coupled with an investigation of classical and modern six‐ to seven‐membered ring‐expansion protocols, which gain access to the central core of these natural products. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Towards the Total Synthesis of Vibsanin E, 15‐O‐Methylcyclovibsanin B,3‐Hydroxyvibsanin E, Furanovibsanin A, and 3‐O‐Methylfuranovibsanin A

et al. 2006

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“…Indium mediated alkyl radical addition to dehydroamino acid derivatives was also reported [54]. The indium-mediated radical ring expansion of -halomethyl cyclic -ketoesters, shown in Scheme 14, was achieved in aqueous alcohols [55]. …”

Section: Indium Mediated Radical Reactions In Aqueous Mediummentioning

confidence: 85%

Recent Advances in Free Radical Chemistry of C-C Bond Formation in Aqueous Media: From Mechanistic Origins to Applications

Perchyonok¹,

Lykakis

2008

MROC

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Recent advances in free radical chemistry have expanded the versatility and flexibility of carbon-carbon bond formation in water or aqueous media. This review highlights the substantial progress, which has been made in the last decade to "tame" the reactive free radical species in aqueous phase reactions. This review focused on recent advances in several classes of widely useful free radical reactions in water leading to the formation of C-C bonds. The review will also explore the recent advances in performing stereo-selective free radical reactions in an aqueous medium and its application in synthesis of natural and unnatural amino acids, preparation of novel materials and solid support chemistry. Some practical hints for help design high yielding free radical reactions in aqueous medium are also presented.In aqueous media carbon centred free radicals are typically generated by either chemical, photolysis or radiolysis methods. These methods are briefly discussed below and the criteria for the selection of a radical initiator and hydrogen donor are discussed in section 3 and 5 respectively.

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“…Previously, we reported Zn-and In-mediated radical ring-expansion reaction of a-halomethyl cyclic b-keto esters in aqueous alcohol to give the corresponding ring-expanded products in good yields, as an environmentally benign method. 15 Here, as a part of our study toward environmentally benign organic synthesis via a radical pathway, 16 we would like to report an efficient, simple, cheap, and environmentally benign Znmediated radical 3-exo-trig cyclization of electron-deficient 2-haloethyl-substituted olefins to provide cyclopropanes in a mixture of t-butyl alcohol and water.As a preliminary study, benzyl 5-bromo-4,4-dimethyl-2-pentenoate (1a-i) and benzyl 5-iodo-4,4-dimethyl-2-pentenoate (1a-ii) were treated with zinc powder in a mixture of t-butyl alcohol and water under refluxing conditions as shown in Table 1. Reactivity of the bromide 1a-i was poor (entries 1-3), even though the reaction was carried out in the presence of KI or under sonication conditions, and the starting material was recovered mainly.…”

mentioning

confidence: 99%

mentioning

confidence: 99%

Facile and Environmentally Benign Zn-Mediated Cyclopropanation of Electron-Deficient 2-Iodoethyl-Substituted Olefins via Radical 3-exo-trigManner

Sakuma¹,

Togo²

2004

Synlett

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An efficient, simple, cheap, and environmentally benign preparation of cyclopropanes via 3-exo-trig manner from various electron-deficient 2-iodoethyl-substituted olefins with zinc powder in a mixture of t-butyl alcohol and water was achieved.The cyclopropane ring is highly strained; nevertheless, a wide variety of naturally occurring cyclopropane derivatives bearing potent utility and biological activity are known. 1 Therefore, synthetic study of the cyclopropane ring is still important. Practical methods for the formation of cyclopropanes with olefinic groups have been carried out with free carbene derived from haloform under basic conditions, 2 diazo-olefins with the Rh-catalyst, 3 the Simmons-Smith reactions 4 and others. 5 These cyclopropanation reactions proceed effectively, especially with the diazo-olefins with the Rh-catalyst and the SimmonsSmith reaction. However, generally electron-rich olefins are required, since these reactions proceed via an electrophilic manner. On the other hand, the formation of cyclopropanes via radical pathways is challenging and interesting, since the cyclopropylmethyl radicals formed via 3-exo-trig manner onto an olefinic group are thermodynamically much disfavored because of their ring strain, 6 and the carbon-centered radicals are generally nucleophilic, and, therefore, electron-deficient olefins are required. 7 Today, to the best of our knowledge, studies on the formation of cyclopropanes via radical 3-exo-trig manner are extremely limited. Thus, for the typical radical reagent system (Bu 3 SnH with AIBN in refluxing benzene), Jung reported an interesting study: the introduction of a gem-dialkoxy group to the 5-position of 6-bromo-2-hexenoate esters dramatically promoted a radical 4-exotrig cyclization to provide the corresponding cyclobutanes (a-cyclobutylacetate esters). 8 Based on this result, methyl 5-bromo-4,4-dimethoxy-2-pentenoate was treated with Bu 3 SnH and AIBN in refluxing benzene. However, the expected cyclopropane derivative was not formed, 9 since ring-opening reaction of the formed cyclopropylmethyl radical occurred rapidly. On the other hand, electrochemical reductive cyclization of ethyl 5-methanesulfonyloxy-4,4-dimethyl-2-pentenoate was effectively carried out to form the corresponding cyclopropane. 10 Photolysis of 2-substituted butyrophenones gave the corresponding cyclopropyl phenyl ketones through a Norrish II-type pathway. 11 A metal-induced radical 3-exo-trig cyclization was reported to occur with chromous acetate, resulting in the formation of 11b-hydroxy-5,9-cyclopregnane-3,20-dione by SET reduction of 9a-bromo-11b-hydroxyprogestrone bearing a d-bromo-a,b-unsaturated ketone group. 12 Treatment of d-iodo-and d-bromo-a,bunsaturated esters with SmI 2 in the presence of t-butyl alcohol in THF gave the corresponding cyclopropanes. 13 The same treatment of g,g-disubstituted d-oxo-a,b-unsaturated esters with SmI 2 in the presence of t-butyl alcohol in THF provided the corresponding cyclopropanols via the ketyl radicals. 14 Among these cyclopropanation...

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Zinc- and Indium-Mediated Ring-Expansion Reaction of α-Halomethyl Cyclic β-Keto Esters in Aqueous Alcohol

Cited by 37 publications

References 48 publications

Towards the Total Synthesis of Vibsanin E, 15‐O‐Methylcyclovibsanin B,3‐Hydroxyvibsanin E, Furanovibsanin A, and 3‐O‐Methylfuranovibsanin A

Towards the Total Synthesis of Vibsanin E, 15‐O‐Methylcyclovibsanin B,3‐Hydroxyvibsanin E, Furanovibsanin A, and 3‐O‐Methylfuranovibsanin A

Recent Advances in Free Radical Chemistry of C-C Bond Formation in Aqueous Media: From Mechanistic Origins to Applications

Facile and Environmentally Benign Zn-Mediated Cyclopropanation of Electron-Deficient 2-Iodoethyl-Substituted Olefins via Radical 3-exo-trigManner

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