Calcium in liquid ammonia for the reduction of benzyl ethers. Mechanistic clues derived from chemoselectivity studies

Hwu, Jih Ru; Chua, Vincent; Schroeder, J.E.; Barrans, Richard E.; Khoudary, Kevin P.; Wang, Naelong; Wetzel, John M.

doi:10.1021/jo00374a048

Cited by 51 publications

(19 citation statements)

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“…17 Our proposal was to incorporate the Tedicyp framework onto an insoluble polymer and thus provide a heterogeneous catalyst that could be isolated from the reaction medium and reused if necessary. The deprotection of benzyl group in ligand 24 can be done by reductive cleavage with calcium in liquid ammonia, 18 or with 6 N hydrochloric acid. 19 A very similar reaction has been reported by Kagan and co-workers.…”

Section: Resultsmentioning

confidence: 99%

Synthesis of cis,cis,cis-1-alkylidene-2,3,4,5-tetrakis(diphenylphosphinomethyl)cyclopentanes

Reynaud¹,

Fall²,

Feuerstein³

et al. 2009

Tetrahedron

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Section: Resultsmentioning

confidence: 99%

Synthesis of cis,cis,cis-1-alkylidene-2,3,4,5-tetrakis(diphenylphosphinomethyl)cyclopentanes

Reynaud¹,

Fall²,

Feuerstein³

et al. 2009

Tetrahedron

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“…calc. for C19H,,04Si (352.55): C 64.73, H 9.15; found: C 64.79, H 8.92.3,7-Anhydro-l,1,2,2-tetradehydro-l,2,6-trideoxy-6-C-ethynyl-~-glycero-~-gulo-octitol(8). At O", a soh.…”

mentioning

confidence: 95%

“…Thiolysis catalysed by BF,.OEt, had been used to cleave acetylenic benzyl ethers [7], but did not prove sufficiently selective, transforming 9 mostly into the fully deprotected 11 (57%), while yielding only 37% of the desired 12. Attempted debenzylation of 9 with Ca/NH, [8] gave a complex mixture. During the synthesis of the monomers [l], however, we had noticed that acetylation by Ac,O in the presence of Me,SiOTf at 0" was accompanied by debenzylation.…”

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confidence: 99%

Oligosaccharide Analogues of Polysaccharides. Part 2. Regioselective deprotection of monosaccharide‐derived monomers and dimers

Alzeer

Vasella

1995

Helvetica Chimica Acta

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The Me$-C( 1) bond of the bis-(trimethylsily1)ethynylated anhydroalditol2 is selectively cleaved with BuLi to yield 3/4, while AgN02/KCN in MeOH cleaves the Me3Si-C(2') bond, leading to 5 (Scheme I ) . Both Me,Si groups are removed with NaOH in MeOH (+ 7), the (i-Pr)$i group is selectively cleaved with HC1 in aq. MeOH (+ 6 ) ; all silyl substituents are removed with Bu,NF (+ 8). Acetolysis transformed 9 into 13, which was desilylated to 14, while thiolysis of 9 led to a mixture 11/12. The tetraacetate 14 has also been obtained from 9 viu 10. Oxidative dimerisation of either 3 or 5, or of a mixture 3/57 yields only the homodimers 15 and 16 (Scheme 2); treatment of 16 with AgN02/KCN yielded 17, deprotection proceeding much more slowly than the cleavage of the Me,Si-C(Z') group of 2. The iodoalkyne 20, required for the cross-coupling with 5 according to Cadiof-Chodkiewicz, was prepared by deprotection of 3/4 to 18, methoxymethylation (+ 19), and iodination. Cross-coupling yielded mostly 21, besides the homodimer 22. Similarly, cross-coupling of 20 and 23 (obtained from 5) led to 24 and 22. The structure of 24 was established by X-ray analysis (Fig.), showing a C(6)-C(5') distance of 5.2 A. The conditions for deprotecting 2 were applied to 21, and led to 25 (AgN02/KCN), 26 (as. NdOH), 27 (Bu,NF), and 29 (HCI/MeOH; Scheme 3). Attempted deprotection of the propargylic-ether moiety with BuLi, however, failed. The dimer 27 was further deprotected to 28. Acetolytic (Ac,O/Me,SiOTf) debenzylation of the dimer 30, obtained from 10, gave 31 (83%) which was deacetylated to 32 (Scheme 4). Cross-coupling of 5 and the bromoalkyne 33, obtained from 10, yielded 34; again, acetolysis proceeded well, leading to 35. The cellobiose derivative 38 was prepared from the lactone 36 via 37. The glycosidic linkage of 38 proved resistant to the conditions of acetolysis, leading to 39. Acetolysis of the benzylated thiophene 40 (from 30 with Na,S) yielded the octaacetate 41, but proceeded in substantially lower yields (50%). J = 11.3, PhCH); 4.84 (d, J = 11.3, PhCH); 4.80 (d, J = 11.3, PhCH); 4.77 (d, J = 11.0, PhCH); 4.60 (d, J = 11.3, PhCH); 4.47 (d, J = 12.1, PhCH); 4.36 (d, J = 12.1, PhCH); 3.99 (dd, J = 9.6, 0.7, H-C(5')); 3.73 (d, J = 9.3, H-C(3)); 3.71 (t, J = 9.6, 9.2, H-C(8)); 3.66 ( t . J =9.3, H-C(4)); 3.65 (dd, J = 11.3, 3.9, H-C(10')); 3.64 (m, H-C(8)); 3.61 (dd, J = 11.1, 1.8, H'-C(lO')); 3.60 (t, J = 9.6, 9.2, H-C(6)); 3.48 (t, J = 9.0, H-C(7')); 3.45 (td, J = 12.4, 5.0, H'-C(8)); 3.22 (ddd, J = 10.4, 8.2, 3.9, H-C(5)); 3.17 (ddd, J = 9.8, 3.7, 1.9, H-C(9')); 2.96 (ddd, J = 10.2, 5.0, 2.3, H-C(7)); 2.53 (br. t, J = 10.3, H-C(6)); 1.88 (d, J =3.9, OH-C(5)); 1.37 (t. J = 6.3, OH-C(8)); 1.34-1.21 (m, (i-Pr),Si); 0.15 (s. Me,Si). 13C-NMR (50 MHz,

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“…The optimal diameter of Pd nanoparticles is approximately 5-8 nm, smaller nanoparticles deactivate faster and are prone to passivation by alkynes whereas larger particles have a smaller fraction of surface atoms. While technological optimisation is far from being exhausted, environmental concerns still persist with respect to the use of lead doped Pd/CaCO 3 catalyst [89][90][91][92].…”

Section: Discussionmentioning

confidence: 99%

The Reduction of Alkynes Over Pd-Based Catalyst Materials - A Pathway to Chemical Synthesis

Ao¹,

Sk²

2017

J Chem Eng Process Technol

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Many reactions, including selective hydrogenation of alkynes, take place on solid surfaces. These reactions are vital in many areas of industry including the manufacture of polymers and fine chemicals such as vitamins, fragrances, and drugs. The choice of a catalyst is a trade-off between activity, selectivity and costs. Palladium-based heterogeneous catalysts are traditionally used for these processes as they provide the activation of hydrogen at room temperatures and offers reasonable selectivity, but these catalysts have a number of practical drawbacks. This review discusses recent research work in the selective hydrogenation of alkynes on palladium-based catalysts, emphasises the mechanism and catalytic materials and important applications including alkyne removal from gasphase alkene precursors for polymer synthesis and liquid phase selective hydrogenation for the synthesis of fine chemicals. Langmuir-Hinshelwood reaction kinetic models, reaction intermediates, formation of carbonaceous layer, the nature of active sites and the effects of reversible and irreversible adsorbates over Pd surface are discussed as well as the factors affecting catalyst activity and selectivity and how these can be optimised in synthetic protocols for these reactions.

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Calcium in liquid ammonia for the reduction of benzyl ethers. Mechanistic clues derived from chemoselectivity studies

Cited by 51 publications

References 1 publication

Synthesis of cis,cis,cis-1-alkylidene-2,3,4,5-tetrakis(diphenylphosphinomethyl)cyclopentanes

Synthesis of cis,cis,cis-1-alkylidene-2,3,4,5-tetrakis(diphenylphosphinomethyl)cyclopentanes

Oligosaccharide Analogues of Polysaccharides. Part 2. Regioselective deprotection of monosaccharide‐derived monomers and dimers

The Reduction of Alkynes Over Pd-Based Catalyst Materials - A Pathway to Chemical Synthesis

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