Synthesis of a Naphtho[2,3-<i>c</i>]pyranone as a Model for the Construction of the Lactone Ring

Hugo, Victor I.; Oosthuizen, Francois J.; Green, Ivan R.

doi:10.1081/scc-120018751

Cited by 6 publications

(3 citation statements)

References 4 publications

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“…Indeed, when the substrate 3l was treated with a stoichiometric amount of CrO 3 , the quinone product 3m was obtained predominantly, with only traces of the desired isochromanone 4l obtained (eq ). Oxidation of p -dimethoxybenzene moieties to quinones is often encountered when using stoichiometric oxidants, such as CAN, MnO 2 , or hypervalent iodine …”

Section: Resultsmentioning

confidence: 99%

Dehydrogenative α-Oxygenation of Ethers with an Iron Catalyst

2014

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Selective α-oxidation of ethers under aerobic conditions is a long-pursued transformation; however, a green and efficient catalytic version of this reaction remains challenging. Herein, we report a new family of iron catalysts capable of promoting chemoselective α-oxidation of a range of ethers with excellent mass balance and high turnover numbers under 1 atm of O2 with no need for any additives. Unlike metalloenzymes and related biomimetics, the catalyst produces H2 as the only byproduct. Mechanistic investigations provide evidence for an unexpected two-step reaction pathway, which involves dehydrogenative incorporation of O2 into the ether to give a peroxobisether intermediate followed by cleavage of the peroxy bond to form two ester molecules, releasing stoichiometric H2 gas in each step. The operational simplicity and environmental friendliness of this methodology affords a useful alternative for performing oxidation, while the unique ability of the catalyst in oxygenating a substrate via dehydrogenation points to a new direction for understanding metalloenzymes and designing new biomimetic catalysts.

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Section: Resultsmentioning

confidence: 99%

Dehydrogenative α-Oxygenation of Ethers with an Iron Catalyst

2014

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“…As described by us [19] as well as other groups [20,21], the MPV reduction of the fluorinated ketone 3ab was affected by the lithium alkoxide generated in situ, but the desired reaction was found to proceed only partially possibly because of the lower reduction ability of the resultant PhCH2CH2OLi (Table1, Entries 1 and 2). In these cases, a small amount of the byproduct was noticed which was considered to be the carboxylic acid 5 possibly formed as a result of the haloform type sequence [20,[25][26][27]. Validity of the i-PrOH addition to this system [19] was noticed to nicely constitute an equilibrium with LiOCH2CH2Ph which afforded i-PrOLi with the higher MPV reduction ability, resulting in formation of 3ab in 60% yield (Entry 3).…”

Section: Reduction Of Ketones Containing Rf Groups By Metal Alkoxidesmentioning

confidence: 99%

Synthesis and synthetic applications of (4-hydroxyphenyl)perfluoroalkylmethanols

Terashima

Kawasaki‐Takasuka

Minami

et al. 2021

Preprint

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Development of the convenient method for the synthesis of (hydroxyphenyl)perfluoroalkylmethanols was achieved by the Meerwein-Ponndorf-Verley (MPV) type reduction of the in situ-generated perfluoroalkylated ketones as the key step, and the benzylic OH group of the resultant alcohols was converted to H or Rf(CH2)nO by way of the corresponding chlorides whose transformation was not easy by any other methods.

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“…to the Fries-Claisen protocol (Scheme 4), yielding advanced product 17 which was then converted by acidmediated lactonization 8 into the known pyranonaphthoquinone 18. 9 The pyranonaphthoquinones are an interesting class of naturally occurring antibiotic compound that also display a wide range of other biological activities, such as antifungal, antiviral, and anticancer activity. 10 Our current work on the application of this novel dual Fries-Claisen rearrangement strategy to the synthesis of pyranonaphthoquinone natural product targets will be reported in due course.…”

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confidence: 99%

Development of a Dual Fries-Claisen Rearrangement Strategy

Duffy

Garcia-Torres

Jones

et al. 2012

Synlett

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In this paper we describe the development and application of a sequential Fries-Claisen rearrangement strategy as a new route for annelation on an aromatic ring. We demonstrate the potential utility of this protocol through the synthesis of a pyranonaphthoquinone target.Whilst the application of double Claisen rearrangements has been investigated by others, 1 including in conjunction with ring-closing metathesis (RCM) methodology, as a method for annelating on a benzene ring, 2 one advantage of developing a process in which different classes of sigmatropic rearrangement are combined and applied consecutively to an aromatic substrate is that of potential differentiation of any resulting (possibly annelated) product. Scheme 1 shows a typical product of double Claisen rearrangement from the work of Kotha. 2 Given the symmetrical nature of the substrate it is clear that this process would not lead to ready differentiation of emerging functionality within the new ring, whereas one can envisage an alternative process in which a dual Fries-Claisen strategy (Scheme 1) could lead to a more flexible target: one in which selective chemistry might then be carried out on the 'upper' or 'lower' edge of the product (as drawn) as the molecular framework is further developed. We now report our progress in developing a unique synthetic strategy based on the coupling of the anionic ortho-Fries and thermal Claisen rearrangements. Individually, the Claisen and anionic ortho-Fries rearrangements 3 are well-known synthetic routes, however, their incorporation into a dual (consecutive) process on the same aromatic substrate has not, to the best of our knowledge, been previously reported, although there has been one report of an unsuccessful attempt to combine and control these useful rearrangements. 4 In this study, Green and co-workers were able to perform a thermally induced Claisen rearrangement on substrate 4, but unfortunately the only product to be isolated in low yield from a subsequent Fries rearrangement of 5 was the furan 6 as a byproduct in a complex mixture, rather than the desired allyl-substituted ketone 7 (Scheme 2). 4 We began our study with an investigation of the rearrangement potential of substrate 8, obtained through a simple two-step procedure from the readily available diol 6-benzyloxy-1,4-dihydroxynaphthalene. 5 We were Scheme 1 A comparison of dual sigmatropic rearrangements, highlighting the opportunity for edge differentiation in a mixed-type rearrangement process O O i) double Claisen ii) methylation OMe OMe RCM OMe OMe R R R R R R O O X Fries-Claisen sequence OMe OMe X annelate OMe OMe X R R R R R R O O O symmetrical "edges" differentiation SYNLETT

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Synthesis of a Naphtho[2,3-c]pyranone as a Model for the Construction of the Lactone Ring

Cited by 6 publications

References 4 publications

Dehydrogenative α-Oxygenation of Ethers with an Iron Catalyst

Dehydrogenative α-Oxygenation of Ethers with an Iron Catalyst

Synthesis and synthetic applications of (4-hydroxyphenyl)perfluoroalkylmethanols

Development of a Dual Fries-Claisen Rearrangement Strategy

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