Samarium Diiodide-Mediated Reductive Coupling of Epoxides and Carbonyl Compounds: A Stereocontrolled Synthesis of C-Glycosides from 1,2-Anhydro Sugars

Chiara, José Luis; Sesmilo, Esther

doi:10.1002/1521-3773(20020902)41:17<3242::aid-anie3242>3.0.co;2-i

Cited by 45 publications

(11 citation statements)

References 55 publications

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“…We next tried titanocene chloride (Cp 2 TiCl) 3a, [11][12][13] as reducing agent, which gave poor results in our previous intermolecular coupling reactions. 4 Thus, addition of a 0.04 M solution of epoxyaldehydes 7 or 8 in tetrahydrofuran to titanocene chloride, prepared in situ by reduction of titanocene dichloride with zinc dust, resulted in the formation of a mixture of tri-and dibenzylated cyclopentitols 13 and 14, respectively, in approximately the same ratio and yield independent of the starting epoxyaldehyde used (Scheme 4). Both products were fully characterized after acetylation of the hydroxy groups.…”

Section: Methodsmentioning

confidence: 98%

“…With our two pairs of epimeric 4-oxiranylcarbonyl substrates at hand, we were ready to investigate the reductive cyclization reaction. Based on our previous results for the intermolecular reductive coupling of epoxides with carbonyl compounds, 4 we first tried to carry out the corresponding intramolecular counterpart under similar reaction conditions, using samarium diiodide as the reducing agent. 10 However, complex reaction mixtures were obtained for all substrates assayed, containing intermolecular pinacol coupling products and iodohydrins, 10 but none of the expected reductive cyclization products.…”

Section: Methodsmentioning

confidence: 99%

“…Our group has recently described the first successful reductive cross coupling of epoxides with aldehydes and ketones 4 promoted by samarium diiodide, for which we proposed an epoxide-derived C-radical of type A as the key reactive intermediate in the C-C bond-forming step. The reaction took place intermolecularly and provided a new access to C-glycosides from 1,2-anhydrohexoses in a stereoselective way, which complemented other approaches previously described.…”

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Stereoselective Synthesis of Branched Cyclopentitols by Titanium(III)-Promoted Reductive Cyclization of 4-Oxiranylaldehydes and 4-Oxiranyl Ketones Derived from Hexoses

Chiara¹,

Bobo²,

Sesmilo³

2008

Synthesis

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Titanocene chloride efficiently promotes the intramolecular reductive cross coupling of highly functionalized 4-oxiranylaldehydes and 4-oxiranyl ketones derived from readily available hexoses affording branched cyclopentitols with good stereoselectivity.Epoxides are a highly valuable and versatile group of compounds widely used in organic synthesis due to their varied reactivity and their straightforward preparation from readily available alkene or carbonyl precursors, generally with high control over their relative and absolute stereochemistry. The strained three-membered oxirane ring is prone to ring-opening reactions with nucleophiles and low-valent-metal reagents. Both types of ring-opening reaction complement each other in terms of polarity and regioselectivity. Thus, while nucleophiles preferentially attack the less substituted carbon of the oxirane ring, single electron transfer from low-valent-metal reagents 1 produce the most substituted b-metal oxide C-radical regioselectively, which subsequently adds to electrophilic radical acceptors.Due to our longstanding interest in the exploration of new strategies for the stereoselective synthesis of highly functionalized cyclitols starting from readily available carbohydrate precursors, 2 we decided to explore the disconnection strategy shown in Scheme 1 for the direct preparation of branched cyclitols of structure I from 4-oxiranylcarbonyl substrates II. A number of possible mechanistic scenarios could be contemplated for the cyclization step, each involving a different generic reactive intermediate A-D. Purportedly, we could envisage the C-C bond-forming step as proceeding through a radical (a, d) or a carbanionic pathway (b, c). In the first case, the required radical intermediates A or D could originate via single electron transfer (SET) reduction of the epoxide or the carbonyl group, respectively. In the ionic alternative, generic carbanionic intermediates B or C could be formed from II either by two sequential SET reductions via radicals A and D or, directly, by a bielectronic process involving the oxidative addition of a low-valent-metal reagent to the epoxide or the carbonyl group. Examples of C-C bond-forming reactions following each of these mechanistic pathways have been described in the literature, 3 with the only exception of path d, which has no precedent.Our group has recently described the first successful reductive cross coupling of epoxides with aldehydes and ketones 4 promoted by samarium diiodide, for which we proposed an epoxide-derived C-radical of type A as the key reactive intermediate in the C-C bond-forming step. The reaction took place intermolecularly and provided a new access to C-glycosides from 1,2-anhydrohexoses in a stereoselective way, which complemented other approaches previously described. With the intention of exploring an intramolecular version of this reaction that could give access to polyoxygenated branched carbocycles, we decided to synthesize appropriate substrates from readily available hexoses.Using D-glucose as the ...

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Section: Methodsmentioning

confidence: 98%

Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

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Stereoselective Synthesis of Branched Cyclopentitols by Titanium(III)-Promoted Reductive Cyclization of 4-Oxiranylaldehydes and 4-Oxiranyl Ketones Derived from Hexoses

Chiara¹,

Bobo²,

Sesmilo³

2008

Synthesis

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“…A two-step/one-pot dimethyl dioxirane oxidation-SmI 2 reduction sequence has been reported with different glycals [183]. Use of this sequence with the ''mannosyl'' derivative 26 and addition to acetone and isobutyraldehyde gave the corresponding a-C-mannopyranosides as the major reaction products with a free OH in position 2 (Scheme 41).…”

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confidence: 99%

The synthesis of d-C-mannopyranosides

Choumane¹,

Banchet²,

Probst³

et al. 2010

Comptes Rendus. Chimie

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“…A variety of efficient methods are available for the synthesis of both O-and C-glycosides. They have contributed enormously to the flexible design of artificial glycoconjugates possessing high medicinal potential (Sears & Wong, 1999;Gruner et al, 2002;Chiara & Sesmilo, 2002). A method used for the synthesis of aryl C-glycosides involves the coupling of 2deoxysugars with phenols in the presence of a trifluoromethylsilyl trifluoromethanesulfonate-silver perchlorate (TMSOTf-AgClO 4 ) catalyst system (Toshima et al, 1998).…”

Section: Commentmentioning

confidence: 99%