Intramolecular iodoetherification of ene or diene ketals: facile synthesis of spiroketals

Fujioka, Hiromichi; Nakahara, Kenji; Hirose, Hideki; Hirano, Kie; Oki, Tomohiro; Kita, Yasuyuki

doi:10.1039/c0cc03933k

Cited by 20 publications

(9 citation statements)

References 40 publications

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“… 35 , 36 Moreover, such complexes are synthetically applicable as halonium transfer and oxidation agents. 29 , 37 − 51 We have shown that the three-center halogen bond has a partial covalent character that increases with the decrease in size of the halogen(I), 25 , 26 an observation recently confirmed by Fourmigué et al 52 Halogen bond strength, however, increases with the size of the halogen and thus with the increase in ionic character (and the decrease in covalent character) of the bond. 26…”

Section: Introductionmentioning

confidence: 76%

Halogen Bond Asymmetry in Solution

et al. 2018

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Halogen bonding is the noncovalent interaction of halogen atoms in which they act as electron acceptors. Whereas three-center hydrogen bond complexes, [D···H···D]+ where D is an electron donor, exist in solution as rapidly equilibrating asymmetric species, the analogous halogen bonds, [D···X···D]+, have been observed so far only to adopt static and symmetric geometries. Herein, we investigate whether halogen bond asymmetry, i.e., a [D–X···D]+ bond geometry, in which one of the D–X bonds is shorter and stronger, could be induced by modulation of electronic or steric factors. We have also attempted to convert a static three-center halogen bond complex into a mixture of rapidly exchanging asymmetric isomers, [D···X–D]+ ⇄ [D–X···D]+, corresponding to the preferred form of the analogous hydrogen bonded complexes. Using 15N NMR, IPE NMR, and DFT, we prove that a static, asymmetric geometry, [D–X···D]+, is obtained upon desymmetrization of the electron density of a complex. We demonstrate computationally that conversion into a dynamic mixture of asymmetric geometries, [D···X–D]+ ⇄ [D–X···D]+, is achievable upon increasing the donor–donor distance. However, due to the high energetic gain upon formation of the three-center-four-electron halogen bond, the assessed complex strongly prefers to form a dimer with two static and symmetric three-center halogen bonds over a dynamic and asymmetric halogen bonded form. Our observations indicate a vastly different preference in the secondary bonding of H+ and X+. Understanding the consequences of electronic and steric influences on the strength and geometry of the three-center halogen bond provides useful knowledge on chemical bonding and for the development of improved halonium transfer agents.

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Section: Introductionmentioning

confidence: 76%

Halogen Bond Asymmetry in Solution

et al. 2018

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“…Cyclic ether 2.31 was obtained by the reaction of 2.30 with PhC(OMe) 3 . 75,76) Alkaline hydrolysis of 2.31 followed by Jones oxidation yielded the cyclic ether 2.32, a civet constituent. Table 1 shows the results of the reactions of ene ketals 2.33 having hydroxyl or carboxylic acid group in the same molecule.…”

Section: Intramolecular Haloetherification Of Ene Acetalsmentioning

confidence: 99%

Development of New Innovative Synthetic Organic Chemistry Using Lone Pairs of Oxygen Atoms

Fujioka

2020

CHEMICAL & PHARMACEUTICAL BULLETIN

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Oxygen atoms have a lone pair of electrons, so they have high chelation ability, high nucleophilic ability, stabilizing ability of adjacent cations, and take a chelate or oxocarbenium ion structure with Lewis acids and metals. I took advantage of these properties to develop three new reactions, 1) asymmetric synthesis of chiral quaternary carbon centers, 2) asymmetric synthesis using acetal functions, and 3) organic chemistry using acetal-type reactive salt chemical species, and applied them to biologically active natural products synthesis. New reactions described here are all innovative and useful for natural products synthesis. In particular, the first asymmetric synthesis of fredericamycin A, and concise asymmetric synthesis of anthracycline antibiotics, scyphostatin, ()-Sch 642305, ()-stenine, clavolonine, ()-rubrenolide, ()-rubrynolide, ()-centrolobine, and decytospolide A and B, etc., are noteworthy. Furthermore, since reactions using acetaltype reactive salt chemical species allow the coexistence of functional groups that normally cannot coexist, the reactions using reactive salts have potential to change the retrosynthesis planned based on conventional reactions.

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“…Pheromone 6 The spirocyclic acetal 8a, prepared using the process depicted in Scheme 4, was subjected to radical reduction conditions. This process (Scheme 5), conducted in water, 7 produced the corresponding methyl-substituted spirocyclic ketal 9, which, when treated with excess cerium(IV) ammonium nitrate (CAN) in MeCN-H 2 O (1:1) underwent oxidative cleavage 8 to directly generate the target pheromone 10 9 through removal of the chiral auxiliary and cyclization to form the ketal moiety.…”

Section: Synthesis Of the Wasp Paravespula Vulgarismentioning

confidence: 99%

Intramolecular Haloetherification of Ene- and Diene-Acetals: Asymmetric Synthesis Involving Chiral Oxonium Ion Intermediates

Fujioka¹

2012

Synlett

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A s y m m e t r i c S y n t h e s i s I n v o l v i n g C h i r a l O x o n i u m I o n I n t e r m e d i a t e sAbstract: Asymmetric processes, taking place via the intermediacy of chiral oxonium ions arising from intramolecular haloetherification reactions of chiral ene-and diene-acetals of optically pure C 2 -symmetric hydrobenzoine, have been developed. A novel, double intramolecular haloetherification process was observed. The asymmetric reactions developed in this effort were applied to the synthesis of several natural products, including solenopsin A, (cis-6-methyltetrahydropyran-2-yl)acetic acid, the pheromone of the wasp Paravespula vulgaris, rubrenolide, rubrynolide, scyphostatin, cryptocaryone, Sch 642305, and clavolonine. The strategies used in these syntheses involved a new concept called 'chiral auxiliary multiple-use methodology'. In addition, intramolecular haloetherification reactions of ene-acetals, derived from chiral optically pure norbornene aldehydes and meso-diols, were applied to asymmetric desymmetrization of meso-diols. Finally, a new method for the resolution of racemic norbornene aldehydes, utilizing chiral ene-acetal oxonium ion intermediates produced from optically pure hydrobenzoin, was developed.

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Intramolecular iodoetherification of ene or diene ketals: facile synthesis of spiroketals

Cited by 20 publications

References 40 publications

Halogen Bond Asymmetry in Solution

Halogen Bond Asymmetry in Solution

Development of New Innovative Synthetic Organic Chemistry Using Lone Pairs of Oxygen Atoms

Intramolecular Haloetherification of Ene- and Diene-Acetals: Asymmetric Synthesis Involving Chiral Oxonium Ion Intermediates

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