Zinc reduction of alkynes

Kaufman, Don; Johnson, Erin R.; Mosher, Michael

doi:10.1016/j.tetlet.2005.06.113

Cited by 19 publications

(4 citation statements)

References 6 publications

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“…(E) More recently, Kaufman 21 disclosed the stereocontrolled dissolving metal reduction of alkynes with activated zinc metal in which product outcome is controlled by the proton source in the reaction.…”

Section: Abstractsmentioning

confidence: 99%

Activated Zinc Dust

Smith¹

2009

Synlett

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This feature focuses on a reagent chosen by a postgraduate, highlighting the uses and preparation of the reagent in current research Activated Zinc DustCompiled by Craig R. Smith Craig R. Smith received his B.S. in Chemistry (2003) and M.S. in Chemistry (2005) from Youngstown State University under the direction of Professor Peter Norris. The same year, he began his Ph.D. studies at The Ohio State University under the supervision of Professor T. V. RajanBabu. Craig has recently received an ACS Organic Division Fellowship (2009). His current interests are the development of new asymmetric transformations and the synthesis of biologically active natural products.

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Section: Abstractsmentioning

confidence: 99%

Activated Zinc Dust

Smith¹

2009

Synlett

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“…The results of this study, while not fully understood, may imply that surface phenomena, together with a relatively slow -forming equilibrium between the intermediate cis and trans anion or radical anion, competes with the rate -determining protonation step in the mechanism. 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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“…[11] Classical hydrogenation with Lindlar catalyst is the easiest way to obtain cis-alkenes, [12] whereas reduction with Li or Na in liquid ammonia is the traditional method for the synthesis of trans-alkenes. [13] However, most of these methods failed to achieve reliable stereoselective partial reduction of 11,12didehydroretinol (6) [14] as an expeditious means of access to 11-cis-and all-trans-retinoids. Thus, although Oroshnik [15] reported that catalytic semihydrogenation of 6 gave 11-cis-retinol (1) in moderate yield, Negishi et al [10a] subsequently found that this reaction could not be performed with high selectivity, and Nakanishi and co-workers [16a] reported that the Lindlar catalyst gave variable results that depended on the level of catalyst "poisoning".…”

Section: Introductionmentioning

confidence: 99%

Synthesis of 11‐cis‐Retinoids by Hydrosilylation–Protodesilylation of an 11,12‐Didehydro Precursor: Easy Access to 11‐ and 12‐Mono‐ and 11,12‐Dideuteroretinoids

Bergueiro

Montenegro

Saá

et al. 2012

Chemistry A European J

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An expeditious, highly efficient approach to 11-cis-retinoids was achieved by semihydrogenation of a readily available 11-yne precursor through a hydrosilylation-protodesilylation protocol. The complete chemo-, regio-, and syn-stereoselectivity of the method also allowed direct access to 11- and 12-monodeutero-, and 11,12-dideutero-11-cis-retinoids. The analogous trans series was not accessible by this route, and was synthesized by means of Hiyama coupling.

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Zinc reduction of alkynes

Cited by 19 publications

References 6 publications

Activated Zinc Dust

Activated Zinc Dust

Dissolving Metals

Synthesis of 11‐cis‐Retinoids by Hydrosilylation–Protodesilylation of an 11,12‐Didehydro Precursor: Easy Access to 11‐ and 12‐Mono‐ and 11,12‐Dideuteroretinoids

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