Asymmetric Synthesis and CD Investigation of the 1,4-Benzodioxane Lignans Eusiderins A, B, C, G, L, and M

Pilkington, Lisa I.; Barker, David

doi:10.1021/jo3015006

Cited by 40 publications

(42 citation statements)

References 34 publications

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“…97 This was achieved using a divergent synthesis, all from the same chiral aldehyde 125, derived from the Mitsunobu coupling of (S)-ethyl lactate 126 and phenol 127, itself synthesised from ovanillin 128 (Scheme 23).…”

Section: Mitsunobu Coupling Of Phenols and Chiral Alcoholsmentioning

confidence: 99%

Synthesis and biology of 1,4-benzodioxane lignan natural products

Pilkington

Barker

2015

Nat. Prod. Rep.

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Section: Mitsunobu Coupling Of Phenols and Chiral Alcoholsmentioning

confidence: 99%

Synthesis and biology of 1,4-benzodioxane lignan natural products

Pilkington

Barker

2015

Nat. Prod. Rep.

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“…18,19 The resulting compounds are 1,7-enynes, which have proved to be valuable synthetic intermediates. 20 Crystal structure of 6ef can be found in the ESI.…”

Section: View Article Onlinementioning

confidence: 99%

Ligand-controlled divergent formation of alkenyl- or allylboronates catalyzed by Pd, and synthetic applications

et al. 2014

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The use of different ligands allows the preparation of either allyl-or alkenylboronates by Pd-catalyzed borylation of allylic carbonates containing alkyne groups. Unprecedented borylative cyclisation to alkenylboronates takes place with PCy 3 . The difficult dissociation of NHC ligands allows borylation of carbonates in the presence of alkynes. Oxidation, regioselective Suzuki coupling, as well as Au-catalyzed cycloisomerisation of boronates illustrate the potential synthetic applications of these reactions.Boronates are important synthetic reagents. They are stable and compatible with most functional groups and are environmentally friendly, tolerating oxygen and water. A wide variety of boronates can be used as nucleophilic partners in Suzuki cross-coupling reactions and allylboronates are reactive towards aldehydes and imines, just to cite the most common uses of these compounds. 1 For this reason, the development of methods for the preparation of boronates, avoiding the use of highly nucleophilic and basic reagents is of main interest. On the other hand, enynes constitute versatile starting materials for the formation of carbo and heterocycles, 2 skeletal rearrangements, 3 and alkoxy-cyclisation, 4 among other reactions. During the last few years, Pd-catalyzed borylative cyclisation reactions of polyunsaturated species have been developed by our group 5-9 and Bäckvall's group, 10 with the aim of preparing cyclized boronates. Our seminal work described an unprecedented preparation of homoallylic boronates starting with 1,6-enynes, in which esters substituting the allylic position were tolerated (Scheme 1, top). 5,11 In our previous studies, addition of ligands precluded the incorporation of the boron substituent. Now, we have found conditions in which the choice of the appropriate ligand allows control of the borylation of alkyne-containing allylcarbonates, affording simple Miyaura coupling to allylboronates, or unprecedented formation of alkenylboronates by borylative cyclisation, a method which is complementary to alkyne hydroboration and the usual reactions of strongly basic Li and Mg nucleophiles with B(OMe) 3 .Thus, we started our study by reacting enynes containing an allylic carbonate group (1). In our previous work mentioned above, 5 we reported that reactions of acetates or other ester derivatives, under ligandless conditions, took place without activation of the C-O bond, leading to homoallylic boronates containing the unreacted ester group (Scheme 1, top). Reactions in the presence of phosphines led to simple cycloisomerisation without incorporation of the boryl group.In contrast, reaction of carbonates 1a-l with B 2 (pin) 2 in the presence of Pd(OAc) 2 and the IMes ligand (formed in situ by deprotonation of the imidazolium chloride with t-BuOK) in xylene, afforded the corresponding allylboronates (Table 1). The reaction is fast (less than 30 min) and takes place under optimum conditions (50 1C) in the absence of added base, as usual for carbonates. A variety of starting compounds showing different ...

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“…, the pair of benzodioxanes 17 and 18 synthesized from (+)-ephedrine; the natural benzodioxanes eusiderin ( 19 ) and eusiderin C ( 20 ) [17]; 21 and 22 , isolated from Juniperus chinensis [18]; and benzodioxane 23 from Licaria chrysophylla [19] (Fig. 5), for both the C-2, C-3 and C-10, C-11 pairs, respectively [20]. …”

Section: Resultsmentioning

confidence: 99%

cis–trans Isomerization of silybins A and B

Novotná

Gažák

Biedermann

et al. 2014

Beilstein J. Org. Chem.

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SummaryMethods were developed and optimized for the preparation of the 2,3-cis- and the 10,11-cis-isomers of silybin by the Lewis acid catalyzed (BF3∙OEt2) isomerization of silybins A (1a) and B (1b) (trans-isomers). The absolute configuration of all optically pure compounds was determined by using NMR and comparing their electronic circular dichroism data with model compounds of known absolute configurations. Mechanisms for cis–trans-isomerization of silybin are proposed and supported by quantum mechanical calculations.

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Asymmetric Synthesis and CD Investigation of the 1,4-Benzodioxane Lignans Eusiderins A, B, C, G, L, and M

Cited by 40 publications

References 34 publications

Synthesis and biology of 1,4-benzodioxane lignan natural products

Synthesis and biology of 1,4-benzodioxane lignan natural products

Ligand-controlled divergent formation of alkenyl- or allylboronates catalyzed by Pd, and synthetic applications

cis–trans Isomerization of silybins A and B

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