A new preparation of 2,5-dihydro-1-benzoxepins using Mitsunobu cyclization, and the synthesis of natural radulanins

Yamaguchi, Seiji; Furihata, Katsunori; Miyazawa, Masaaki; Yokoyama, Hajime; Hirai, Yoshiro

doi:10.1016/s0040-4039(00)00676-6

Cited by 32 publications

(17 citation statements)

References 13 publications

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“…[32] This system has also been formed as minor byproducts of radical homoallylation, [33] insertion of a triple bond into a C À H bond of an olefin in arene-chromium tricarbonyl complexes, [34] and Pd-catalyzed annulation of O-substituted 1,3-dienes. [35] Asymmetric synthesis of trans-pterocarpin: The last stage was to check the applicability of the method to the asymmetric total synthesis of natural pterocarpans.…”

Section: Full Papermentioning

confidence: 99%

Silver‐Catalyzed Asymmetric Synthesis of 2,3‐Dihydrobenzofurans: A New Chiral Synthesis of Pterocarpans

Jiménez-González

García-Muñoz

Álvarez-Corral

et al. 2006

Chemistry A European J

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2,3-Dihydrobenzofurans can be diastereoselectively prepared by condensation of aromatic aldehydes with 2,3-dihydrobenzoxasilepines under the catalysis of Ag(I) complexes, and in the presence of a source of fluoride ion. The application of this strategy by using chiral catalysts leads to a new enantioselective total synthesis of natural cis-pterocarpans and their trans isomers. Through this method, the first enantioselective total synthesis of the antifungal agent (-)-pterocarpin was achieved. In addition, a new entry into the heteroaromatic system of 2,5-dihydrobenzoxepine is also presented.

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Section: Full Papermentioning

confidence: 99%

Silver‐Catalyzed Asymmetric Synthesis of 2,3‐Dihydrobenzofurans: A New Chiral Synthesis of Pterocarpans

Jiménez-González

García-Muñoz

Álvarez-Corral

et al. 2006

Chemistry A European J

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“…gave the corresponding diols 4a (52% yield), 4b (52%), 4c (72%), and 4d (86%). Mitsunobu cyclization [7] [8] of diols 4a ± 4d by treating with Ph 3 P and diethyl azodicarboxylate (DEAD) in dry THF gave 5a (68% yield), 5b (72%), 5c (85%), and 5d (91%), respectively. In this cyclization, the absolute configuration was converted completely by an S n 2-type nucleophilic displacement.…”

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confidence: 99%

Synthesis of Both Enantiomers of Flavanone and 2-Methylchromanone

Noda¹,

Watanabe²

2002

HCA

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“…[97][98][99][100][101][102][159][160][161][162] These structures present unique opportunities in organic synthesis. 20 170 and an unattractive tin reagent 20,103,169 towards the total synthesis of these natural products. Radulanin A (83) specifically not only represents a simplified target for an initial synthesis but also a viable target on which to utilize an array of organophosphorus methodologies developed in the Wiemer lab.…”

Section: Chapter IV Synthesis Of Radulanins Through Organophopshorus mentioning

confidence: 99%

“…followed by cyclization using Mitsunobu conditions afforded the natural product radulanin A in 12 steps and an overall 8% yield. 20,103 An alternative cyclization also was attempted through a ZnCl 2 mediated process, 107 but only starting material was isolated 75 ( Figure 59). It is possible that the metal reagent was no longer anhydrous and therefore recrystallized ZnCl 2 would need to be used in future efforts.…”

Section: Chapter IV Synthesis Of Radulanins Through Organophopshorus mentioning

confidence: 99%

“…This is not surprising since the literature demonstrates good yields when the reaction is performed at reflux. 20,96,103 Oxidation of the EAS product followed by a deprotection could lead to the synthesis of radulanin E. Initial oxidation efforts conducted on a very small scale provided only starting material. The model substrate 241…”

Section: Chapter IV Synthesis Of Radulanins Through Organophopshorus mentioning

confidence: 99%

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New synthesis and reactions of phosphonates

Richardson¹

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The importance of phosphorus can be highlighted not only through its biological significance, but also in its many varied industrial, medicinal, and synthetic applications.Phosphonate moieties in particular have broad applications including their use as reagents in the Horner-Wadsworth-Emmons olefination reaction, a widely used synthetic strategy.As an alternative to the often harsh conditions required for phosphonate synthesis, a mild and versatile one-flask protocol has been developed in which a benzylic alcohol can be directly converted to the diethyl benzylphosphonate ester. Moreover, this zinc iodide mediated process provides good yields on both small and larger scale reactions.Explorations into this unique transformation with non-racemic substrates revealed that the reaction may proceed through an S N 1-like mechanism.The new phosphonate methodology has been utilized successfully on allylic, heterocyclic, and both electron poor and rich benzylic systems. This allows the synthesis of many types of dialkyl benzylphosphonate esters. Specific examples include compounds used towards the synthesis of natural product analogues and at least one phosphonate ester not previously attainable under standard conditions. Isotopic labelling experiments provided additional mechanistic insight suggesting a probable carbocation process. The mild and facile reaction conditions and the good yields of diverse, complex phosphonate products emphasize the broad applicability of this protocol.To demonstrate the utility of this phosphorus-based methodology, synthetic sequences and Lewis acid-mediated cascade cyclizations towards the synthesis of natural products have been developed. The natural radulanins, isolated from liverworts, possess a plethora of biological properties and present the opportunity to utilize and expand upon many aspects of this research. Formation of the benzoxepin core of the radulanins through a Lewis acid-mediated cyclization ultimately led to the total synthesis of radulanin A. An additional product consisting of cyclization with electrophilic aromatic 2 substitution of a methoxymethyl substituent originating in the MOM-protecting group also was discovered, leading to a highly substituted benzoxepin that should be of value in the synthesis of radulanin E. Abstract Approved:Thesis Supervisor

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A new preparation of 2,5-dihydro-1-benzoxepins using Mitsunobu cyclization, and the synthesis of natural radulanins

Cited by 32 publications

References 13 publications

Silver‐Catalyzed Asymmetric Synthesis of 2,3‐Dihydrobenzofurans: A New Chiral Synthesis of Pterocarpans

Silver‐Catalyzed Asymmetric Synthesis of 2,3‐Dihydrobenzofurans: A New Chiral Synthesis of Pterocarpans

Synthesis of Both Enantiomers of Flavanone and 2-Methylchromanone

New synthesis and reactions of phosphonates

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