Ab Initio Study of Intramolecular Ring Cyclization of Protonated and BF3-Coordinated trans- and cis-4,5-Epoxyhexan-1-ol

Coxon, James M.; Thorpe, Aaron J.

doi:10.1021/jo990364d

Cited by 13 publications

(11 citation statements)

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“…Coxon et al recently reported an ab initio study of the intramolecular ring cyclization of protonated and BF 3 ‐coordinated cis ‐4,5‐epoxyhexan‐1‐ol 25. The potential energy surface for the rearrangement of protonated epoxy alcohols shows activation barriers much more favorable to five‐membered transition structures leading to furan.…”

Section: Resultsmentioning

confidence: 99%

Direct Access to Furanosidic Eight‐Membered Ulosonic Esters from cis‐α,β‐Epoxy Aldehydes

Sugisaki

Ruland²,

Baltas

2003

Eur J Org Chem

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Direct access to bicyclic precursors of octulosonic acids is achieved by treatment of differentially (or not) protected γ,δ‐bis(silyloxy) cis‐α,β‐epoxy aldehydes with ethyl 2‐(trimethylsilyloxy)‐2‐propenoate in the presence of boron trifluoride−diethyl ether. An X‐ray crystallographic structure of a bicycle (compound 33a) was obtained and used to determine the absolute configurations of the different stereogenic centers and thus the diastereoselective preference of the aldol reaction (syn) and the regioselectivity of the epoxide ring‐opening (C‐6 atom). Functionalization and opening of the bicyclic compound to afford octulosonic analogues in their furanoside forms was studied. An octulosonic 8‐phosphate analogue has been synthesized. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

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Section: Resultsmentioning

confidence: 99%

Direct Access to Furanosidic Eight‐Membered Ulosonic Esters from cis‐α,β‐Epoxy Aldehydes

Sugisaki

Ruland²,

Baltas

2003

Eur J Org Chem

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“…[25] The potential energy surface for the rearrangement of protonated epoxy alcohols shows activation barriers much more favorable to five-membered transition structures leading to furan. [25] The potential energy surface for the rearrangement of protonated epoxy alcohols shows activation barriers much more favorable to five-membered transition structures leading to furan.…”

Section: Mukaiyama Aldol Reactionsmentioning

confidence: 99%

Direct Access to Furanosidic Eight‐Membered Ulosonic Esters from cis‐α,β‐Epoxy Aldehydes.

2003

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Carbohydrates Carbohydrates U 0500Direct Access to Furanosidic Eight-Membered Ulosonic Esters from cis-α,β-Epoxy Aldehydes. -Mukaiyama aldol reaction of cis-α,β-epoxy aldehydes (I) with α-siloxypropenoate (II) in the presence of Lewis acid BF3·OEt2 provides access to bicyclic precursors of octulosonic acids (III)/(IV). The aldol reaction proceeds with syn-selectivity. Similar result is obtained from the threo-analogues of aldehydes (I). As demonstrated for bicyclic compound (IIIb), acidic cleavage of the bicyclic structure provides the octulosonic acid derivatives [cf. (V)], which can be further functionalized. A variety of functionalized bicyclic precursors (IX) is also tested in acidic ring opening. It is shown, however, that the free endocyclic hydroxyl group is crucial for successful ring opening, since derivatives (IX) do not afford the expected octulosonic acid derivatives. -(SUGISAKI, C. H.; RULAND, Y.; BALTAS*, M.; Eur.

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“…3). This structural change in turn alters the trajectory of the nucleophile toward the epoxide electrophile, a factor that computations suggest is most important for selectivity in epoxide-opening reactions (27,28). Because the template of 1b cannot participate in similar hydrogen-bonding interactions, an unselective reaction proceeds with the template in the more stable chair conformation.…”

Section: Resultsmentioning

confidence: 99%

Entropic factors provide unusual reactivity and selectivity in epoxide-opening reactions promoted by water

Byers

Jamison

2013

Proc. Natl. Acad. Sci. U.S.A.

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Despite the myriad of selective enzymatic reactions that occur in water, chemists have rarely capitalized on the unique properties of this medium to govern selectivity in reactions. Here we report detailed mechanistic investigations of a water-promoted reaction that displays high selectivity for what is generally a disfavored product. A combination of structural and kinetic data indicates not only that synergy between substrate and water suppresses undesired pathways but also that water promotes the desired pathway by stabilizing charge in the transition state, facilitating proton transfer, doubly activating the substrate for reaction, and perhaps most remarkably, reorganizing the substrate into a reactive conformation that leads to the observed product. This approach serves as an outline for a general strategy of exploiting solvent-solute interactions to achieve unusual reactivity in chemical reactions. These findings may also have implications in the biosynthesis of the ladder polyether natural products, such as the brevetoxins and ciguatoxins.entropic control | biomimetic G iven its simple structure and low molecular weight, water is a remarkably complex substance. Several landmark investigations (1) have revealed the ability of water to self-assemble to form sophisticated dynamic hydrogen bond networks, which accounts for its unusual properties, such as its high boiling point and high surface tension (2). Despite the unique properties that it offers and that nature has exploited, water is generally eschewed in synthetic chemistry largely because of chemical incompatibility with many commonly used reagents and the low aqueous solubility of many organic molecules coupled with the attendant assumption that homogeneity is required for reactivity. Although several important examples of remarkable reactivity have been documented for reactions carried out in water (3-5), on the surface of water (6, 7), or in micelles suspended in water (8, 9), utilization of the "biological solvent" in organic reactions remains uncommon.We became acutely aware of the remarkable properties of water when we discovered that neutral aqueous solutions of epoxy alcohol 1a underwent a spontaneous and selective "endo" cyclization reaction to form 6,6-fused bicyclic product 2a (Fig. 1) (10-12). Exceptional reactivity and selectivity were observed only when two criteria were satisfied: The substrate contained a sixmembered tetrahydropyran ring, and the solvent used was water at pH 7.0. These surprising results were counter to a set of general empirical rules put forth by Baldwin for cyclization reactions, which state that the smaller ring product resulting from what is commonly called an exo cyclization is favored for similar reactions (13). The tetrahydropyranol ring, therefore, appeared to "template" the endo cyclization pathway to form the larger ring product with water playing a critical yet heretofore unknown role.Moreover, 2a is a substructure found in a large family of natural products commonly referred to as the ladder polyethers (e....

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Ab Initio Study of Intramolecular Ring Cyclization of Protonated and BF₃-Coordinated trans- and cis-4,5-Epoxyhexan-1-ol

Cited by 13 publications

References 13 publications

Direct Access to Furanosidic Eight‐Membered Ulosonic Esters from cis‐α,β‐Epoxy Aldehydes

Direct Access to Furanosidic Eight‐Membered Ulosonic Esters from cis‐α,β‐Epoxy Aldehydes

Direct Access to Furanosidic Eight‐Membered Ulosonic Esters from cis‐α,β‐Epoxy Aldehydes.

Entropic factors provide unusual reactivity and selectivity in epoxide-opening reactions promoted by water

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