Selective Reduction of Terminal Alkynes to Alkenes by Indium Metal

Ranu, Brindaban C.; Dutta, Joy; Guchhait, Sankar K.

doi:10.1021/jo010262z

Cited by 24 publications

(8 citation statements)

References 20 publications

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“…Moreover, the triple bond in aryl propargyl ethers, amines, and esters could be selectively reduced to the double bond by refluxing the substrates in aqueous ethanol in the presence of indium previously activated by sonication (Scheme 59). 173 Non-functionalized and internal alkynes were stable under the employed conditions. Although alkyl derivatives were very reluctant to undergo this reaction and the reaction times required were comparably long (>40 h) this transformation turned out to be synthetically valuable since no overreduction occurred, the procedure was compatible with several other easily reducible functionalities and the yields were usually high.…”

Section: Reduction Of Carbon-carbon Triple Bondsmentioning

confidence: 97%

Indium in Organic Synthesis

Podlech¹,

Maier²

2003

Synthesis

245

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Section: Reduction Of Carbon-carbon Triple Bondsmentioning

confidence: 97%

Indium in Organic Synthesis

Podlech¹,

Maier²

2003

Synthesis

245

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“…Thus, whereas in the presence of HCl as the acid, the trans isomer (57) is the major reaction product, the corresponding cis isomer (58) is obtained when AcOH is used as the proton source (Scheme 17.21 ) [65] . Highly selective reduction of terminal alkynes to alkenes in aryl propargyl ethers, amines and esters has been achieved using In metal in aqueous ethanol without formation of undesired side -reactions such as over -reduction of the double bond formed [66] .…”

Section: Reduction Of C ∫ C Bondsmentioning

confidence: 99%

Dissolving Metals

Yus

Foubelo

2008

Modern Reduction Methods

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17 IntroductionDissolving metals have been used extensively as reducing agents for more than a century but today they have been partially displaced from the central fi eld of organic synthesis by the use of other more selective methodologies, such as metal hydrides [1] and catalytic hydrogenations [2] . However, dissolving metals are still of interest for the selective reduction of specifi c polar functional groups (such as hindered cyclic ketones) and the reductive cleavage of some activated bonds [3] .Regarding the mode of action of electropositive metals in reduction processes, it is generally assumed that an initial single -electron transfer ( SET ) from the metal to the organic substrate takes place to give a radical anion [4] . Depending on the organic substrate and on the reaction conditions (mostly on the solvent), the highly reactive resulting radical anion can then decompose via a number of different routes. For instance, for compounds (I) with multiple C = X bonds (X = CR 2 , O, NR, S), the radical anion (II) could be protonated in the presence of a proton source (the solvent) to give a new radical (III) , which after a further SET from the metal, and further protonation of the resulting anion (IV) , would lead to the reduced product (V) . In the absence of a proton source, coupling of two radical anions (II) can occur to give fi rst the dianionic species (VI) and, after hydrolysis, compounds of type (VII) . Organic substrates (VIII) with activated bonds X − Y (X = CR 3 , OR, SR, NR 2 ; Y = CR 3 , OR, SR, NR 2 , Hal (F, Cl, Br, I)) also undergo reductive cleavage by means of electropositive metals through a SET mechanism. In this case, the initially formed radical anion (IX) suffers the activated X − Y bond scission to generate a radical (X) and an anion (XI) . Radical (X) would be converted to an anion after a new electron transfer from the metal, and fi nal protonation would yield the corresponding reduced products (XII) and (XIII) , respectively (Scheme 17.1 ).Most of the reductions by means of dissolving metals have been performed using highly electropositive metals, such as Li, Na and K, in liquid NH 3 as solvent. Less electropositive metals (Mg, Ca, Sr, Ba, Ni, Cu, Zn, In, Sn, Pb) have also been used, so by choosing the appropriate metal, solvent and cosolvent it is possible to

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“…Since the ionization potential is directly associated with the capability of the metal to release electrons, indium-mediated reactions apparently proceed by a single-electron transfer (SET) mechanism and the metal has been used as a mild potential reducing agent for a number of useful transformations. Some of the important reactions include stereoselective reductive elimination of 1,2-dibromides to give trans-alkenes, [5] reduction of terminal alkynes to alkenes, [6] reduction of C=C bonds in activated conjugated alkenes, [6] and selective reductions of the heterocyclic rings in quinolines and quinoxalines [7] and of aromatic nitro groups. [7] In continuation of our ongoing research program, we became interested in norbornyl-based acyloins possessing bridgehead halogens.…”

Section: Introductionmentioning

confidence: 99%

Indium‐Mediated Regio‐ and Diastereoselective Reduction of Norbornyl α‐Diketones

Khan

Sudheer

2004

Chemistry A European J

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A novel, efficient, and regio- as well as diastereoselective conversion of non-enolizable bicyclic alpha-diketones into synthetically useful acyloins mediated by indium metal is described. The reduction is highly diastereoselective, leading exclusively to endo-acyloins (endo-hydroxyl groups) in excellent yields, and tolerates a variety of sensitive substituents, such as acetate, ester, and bridgehead halogens. The regioselectivity in the reductions of monosubstituted alpha-diketones varied from 70:30 to 100:0 for the two possible isomeric alcohols. The methodology is extended to the synthesis of highly functionalized cyclopentane carboxaldehydes, potential building blocks in organic syntheses, by cleavage of the acyloins by treating them with Pb(OAc)4 in MeOH/PhH. Allylindium additions to carboxaldehydes 22 have been found to be highly diastereoselective.

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Selective Reduction of Terminal Alkynes to Alkenes by Indium Metal

Cited by 24 publications

References 20 publications

Indium in Organic Synthesis

Indium in Organic Synthesis

Dissolving Metals

Indium‐Mediated Regio‐ and Diastereoselective Reduction of Norbornyl α‐Diketones

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