A novel stereospecific reduction of alkynes to alkenes

Sondengam, B.L.; Charles, G.; Akam, Thomas M.

doi:10.1016/s0040-4039(00)78841-1

Cited by 36 publications

(11 citation statements)

References 6 publications

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“…This confirms that MeOH can act as a H 2 source in this reaction, although H 2 itself is more efficient. Similar reactivity has been seen before 16 and recently a Ni(0) phosphine complex was shown to behave in the same way. 17…”

Section: Reactivity Studies Employing [Pt( T Bucope)(chphch 2 Ph)] (O...supporting

confidence: 84%

A parahydrogen based NMR study of Pt catalysed alkyne hydrogenation

et al. 2010

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Section: Reactivity Studies Employing [Pt( T Bucope)(chphch 2 Ph)] (O...supporting

confidence: 84%

A parahydrogen based NMR study of Pt catalysed alkyne hydrogenation

et al. 2010

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“…The attempted (Z-selective) semi-hydrogenation of the hindered alkyne unit, in the case of 10a and some of its derivatives, proved to be difficult. Various methods (such as H 2 , Lindlar catalyst; [16] H 2 , P-2 Ni; [17] H 2 , Zn-Cu couple; [18] 9-borabicyclo[3.3.1]nonane (9-BBN-H), protonolysis [19] ) failed completely (no conversion). Finally, it was found that the transformation could be achieved by using NaBH 4 in PEG 200 and CH 2 Cl 2 in the presence of 10 mol-% PdI 2 (or PdCl 2 ).…”

Section: Resultsmentioning

confidence: 99%

Stereoselective Synthesis and Biological Evaluation of Ferrocene‐Containing 5‐Hydroxyeicosatetraenoic Acid Analogues

et al. 2011

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The stereoselective synthesis of a set of four stable 5-hydroxyeicosatetraenoic acid (HETE) analogues with a ferrocene backbone is described. The common substructure of all HETEs, the (2E,4Z)-1-hydroxyhexadiene moiety, was formally replaced by a ferrocenylmethanol fragment. Whereas the hydrophilic side chain remained the same as that of 5-HETE (butyrate), the lipophilic side chain was simplified by replacing the "natural" (Z,Z)-1,4-decadiene side chain with (Z)-1-heptene, 1-heptyne, 1-octyne, or phenylacetylene. As a key building block, Kagan's chiral acetal (derived from ferrocenecarbaldehyde) was used for the stereoselective generation of the planar-chiral substructure through diastereoselective ortho-lithiation and subsequent formylation, methoxycarbonylation or iodination, respectively. The lipophilic side chain was installed either by a "salt-free" Wittig reaction or (better) by Pd-catalyzed Sonogashira coupling. The

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“…The same reductions in the absence of a proton source result in a mixture of trans -and cis -isomers after hydrolysis. However, the reduction with the Zn/Cu couple in MeOH leads predominantly to cis -alkenes through a different mechanism, which has not yet been determined [63] .…”

Section: Reduction Of C ∫ C Bondsmentioning

confidence: 95%

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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A novel stereospecific reduction of alkynes to alkenes

Cited by 36 publications

References 6 publications

A parahydrogen based NMR study of Pt catalysed alkyne hydrogenation

A parahydrogen based NMR study of Pt catalysed alkyne hydrogenation

Stereoselective Synthesis and Biological Evaluation of Ferrocene‐Containing 5‐Hydroxyeicosatetraenoic Acid Analogues

Dissolving Metals

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