Vitamin B129 a catalyst in the synthesis of prostaglandins

Busato, Stephan; Tinembart, O.; Zhang, Zhong-da; Scheffold, Rolf

doi:10.1016/s0040-4020(01)85455-7

Cited by 86 publications

(39 citation statements)

References 38 publications

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“…Thus, knowing kobs z k,, k, is indirectly obtained by Eqn. 4 ( Table 2). The activation energy of the formation of 6 at [El = 1~ and E = 40 is AG&3K = 86 f 5 kJ.mol-'.…”

Section: Meric (1r2r)-and (1 S2s)-co~-(2-hydroxycyclopentyl)cob(iiimentioning

confidence: 99%

“…in the exceedingly simple cob(1)alamin-catalyzed isomerization might be tolerated, if the enantiomerically enriched alcohol may be transformed efficiently to pure (crystalline) compounds as, e.g., in the three-step synthesis of the enantiomerically pure prostaglandin intermediate (+)-(3aS,6aR)-3,3a,6,6a-tetrahydro-2H-cyclopenta[b]furan-2-one, obtained in 32 % overall yield from ( R ) -cyclopent-2-en01 (e.e. 62%) [4].…”

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confidence: 99%

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Asymmetric Catalysis by Vitamin B₁₂. The Mechanism of the Cob(I)alamin‐Catalyzed Isomerization of 1,2‐Epoxycyclopentane to (R)‐Cyclopent‐2‐enol

Bonhôte

Scheffold

1991

Helvetica Chimica Acta

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The isomerization of 1,2-epoxycyclopentane (1) to enantiomerically enriched (R)-cyclopent-2-enol (2) in protic solvents is catalyzed by coh(1)abdmin. The enantiomeric excess (e.e.) of (R)-2 is usually ca. 60%; it is only slightly dependent on the temperature, hut increases with decreasing dielectric constant E of the solvent. Standard kinetic methods show the reaction to be first order in vitamin B,, and zero order in 1. The rate constant increases exponentially with increasing E of the solvent. An Arrhenius plot at E = 40 gives activation parameters A H f = 78 + 4 kJ.mol-I and A S f = -49 ! C 1 J.mo1-I.K-l. The isomerization 1 + 2 proceeds in two steps (Schemes 2 and 7): i) The epoxide ring is first opened by the proton-assisted fast and irreversible nucleophilic attack of the chiral Co' catalyst to form diastereoisomeric (1 R,2R)-and (lS,2S)-(2-hydroxycyclopentyl)cob(III)alamins 6 in a ratio of ca. 4:l which are the dominant species in the steady state; ii) The intermediates 6 then decompose in the rate-limiting step to form 2 and recycled catalyst. Experiments with specifically 'H-labeled 1 showed the hydro-cobalt elimination 6 -+ 2 to be non-stereoselective. It proceeds via reversible Co-C bond homolysis to a free 2-hydroxycyclopentyl radical from which stereoelectronically controlled H-abstraction by Co" takes place.

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“…Thus, knowing kobs z k,, k, is indirectly obtained by Eqn. 4 ( Table 2). The activation energy of the formation of 6 at [El = 1~ and E = 40 is AG&3K = 86 f 5 kJ.mol-'.…”

Section: Meric (1r2r)-and (1 S2s)-co~-(2-hydroxycyclopentyl)cob(iiimentioning

confidence: 99%

mentioning

confidence: 99%

Asymmetric Catalysis by Vitamin B₁₂. The Mechanism of the Cob(I)alamin‐Catalyzed Isomerization of 1,2‐Epoxycyclopentane to (R)‐Cyclopent‐2‐enol

Bonhôte

Scheffold

1991

Helvetica Chimica Acta

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“…Desymmetrization of the meso-cyclopentane-3,5-diacetate 110 by enzymatic hydrolysis according to the procedure of Schefold [49], yielded alcohol 111 in 95% ee (Scheme 23). Protection of 111 followed by ozonolysis and NaBH4 reduction gave the diol 112.…”

Section: Ghosh's Synthesis Of Madumycin IImentioning

confidence: 99%

Chemistry and Biology of the Streptogramin A Antibiotics

Ahmed¹,

Donaldson²

2007

MROC

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“…which the attack of the potential radical to a C,C-multiple bond occurs by a 5-, 6-or 7-e~o-and a 6-or 7-endo~mode. As an example the synthesis of a bicyclic lactol (an intermediate in prostaglandin synthesis [12]) is described (scheme) [13]. The consecutive formation of more than one C,C-bond in one operation may occur, if a set of structural elements like R-X and more than one C,C-multiple bond' are properly arranged for inter-and intramolecular addition.…”

Section: B12-catalyzed Intermolecular Addition [1 3 4jmentioning

confidence: 99%

“…B 12 -catalyzed tandem-reactions have been applied in the synthesis of brasilenol [14](for an independent synthesis cf. [15]) and the key-intermediate of PGF 2 [13](for related syntheses cf. [16])(scheme).…”

Section: B12-catalyzed Intermolecular Addition [1 3 4jmentioning

confidence: 99%

Vitamin B12, Catalyst of Radical Reactions in Organic Synthesis

Scheffold

Busato

Eichenberger

et al. 1988

Organic Free Radicals

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Vitamin B12 and related metal complexes act as mediators in the electron transfer from the electron source (chemical reducing agent or cathode in electrochemical reductions) to an electrophilic substrate R-X (R-X = alkyl-, vinyl-or acyl-derivative) [IJ. On B 12 -catalyzed reduction R-X is transformed to the radical R' or the carbanion R-(depending on the structure of R and the reaction conditions) either directly or via an organometallic intermediate. The vitamin B 12 -catalyzed electrolysis of R-X at ca. -0.9 V vs.SCE under simultaneous irradiation of visible light [4J is the mildest way to form radicals R' by umpoZung of R-X. The thus created radicals may undergo follow-up reactions 'as e.g.: intra-or intermolecular addition to olefins [5J, elimination of a-leaving groups [6J, reduction followed by protonat,ion [7], disproportionation to olefin and hydrocarbon [BJ or rearrangements [9J.To the synthetically most useful reactions belongs the the C,C-bond formation by inter-or intramolecular addition to the (activated) double or triple bond of alkenes or alkines as well as the (concerted) formation of more than one C,C-bond by subsequent inter-or intramolecular additions (tandem-reaction).The application of the Organic Photo Electro Catalysis (OPEC-reaction) with B12 as catalyst is illustrated by the synthesis of some natural products. B12-catalyzed intermolecular addition [1, 3, 4JAs an example the synthesis of all stereoisomers of brevicomin (an insect pheromon) starting from cheap enantiomerically pure compounds like tartaric acid, mannitol, vitamin C and ribonolactone is described [10J. The strategy for the construction of bicyclic ketales is outlined in the scheme.

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Vitamin B129 a catalyst in the synthesis of prostaglandins

Cited by 86 publications

References 38 publications

Asymmetric Catalysis by Vitamin B₁₂. The Mechanism of the Cob(I)alamin‐Catalyzed Isomerization of 1,2‐Epoxycyclopentane to (R)‐Cyclopent‐2‐enol

Asymmetric Catalysis by Vitamin B₁₂. The Mechanism of the Cob(I)alamin‐Catalyzed Isomerization of 1,2‐Epoxycyclopentane to (R)‐Cyclopent‐2‐enol

Chemistry and Biology of the Streptogramin A Antibiotics

Vitamin B12, Catalyst of Radical Reactions in Organic Synthesis

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Vitamin B129 a catalyst in the synthesis of prostaglandins

Cited by 86 publications

References 38 publications

Asymmetric Catalysis by Vitamin B12. The Mechanism of the Cob(I)alamin‐Catalyzed Isomerization of 1,2‐Epoxycyclopentane to (R)‐Cyclopent‐2‐enol

Asymmetric Catalysis by Vitamin B12. The Mechanism of the Cob(I)alamin‐Catalyzed Isomerization of 1,2‐Epoxycyclopentane to (R)‐Cyclopent‐2‐enol

Chemistry and Biology of the Streptogramin A Antibiotics

Vitamin B12, Catalyst of Radical Reactions in Organic Synthesis

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Asymmetric Catalysis by Vitamin B₁₂. The Mechanism of the Cob(I)alamin‐Catalyzed Isomerization of 1,2‐Epoxycyclopentane to (R)‐Cyclopent‐2‐enol

Asymmetric Catalysis by Vitamin B₁₂. The Mechanism of the Cob(I)alamin‐Catalyzed Isomerization of 1,2‐Epoxycyclopentane to (R)‐Cyclopent‐2‐enol