A formal synthesis of aflatoxin B2: a Dötz benzannulation approach

Eastham, Stephen A.; Ingham, Steven P.; Hallett, Michael R.; Herbert, John M.; Quayle, Peter; Raftery, James

doi:10.1016/j.tetlet.2006.02.024

Cited by 30 publications

(6 citation statements)

References 80 publications

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“…In contrast, attempts to synthesize the corresponding biphenol or benzoxepine under our standard conditions afford silylether 11 as the major product (entries 3 and 4). Mechanistically, the isomerization of 9 to 11 involves a 1,3-silatropic rearrangement (Brook rearrangement), which is known for ortho- silyl phenols, but only at elevated temperatures (>100 °C) or in the presence of trace acid . Under our catalytic aerobic conditions, isomerization is complete within 1 h at room temperature.…”

Section: Resultsmentioning

confidence: 84%

Controlling the Catalytic Aerobic Oxidation of Phenols

et al. 2014

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The oxidation of phenols is the subject of extensive investigation, but there are few catalytic aerobic examples that are chemo- and regioselective. Here we describe conditions for the ortho-oxygenation or oxidative coupling of phenols under copper (Cu)-catalyzed aerobic conditions that give rise to ortho-quinones, biphenols or benzoxepines. We demonstrate that each product class can be accessed selectively by the appropriate choice of Cu(I) salt, amine ligand, desiccant and reaction temperature. In addition, we evaluate the effects of substituents on the phenol and demonstrate their influence on selectivity between ortho-oxygenation and oxidative coupling pathways. These results create an important precedent of catalyst control in the catalytic aerobic oxidation of phenols and set the stage for future development of catalytic systems and mechanistic investigations.

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Section: Resultsmentioning

confidence: 84%

Controlling the Catalytic Aerobic Oxidation of Phenols

et al. 2014

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“…At this moment two possible scenarios explaining the observed desilylation are feasible: 1) Intramolecular silyl transfer–a [1,3]-silatropic rearrangement can be attributed to this issue. For example, a [1,3]-Brook rearrangement 13 of ortho -silyl phenols to afford silyl ethers has been reported, however, this process was explored mainly under acidic conditions, 14 elevated temperatures 15 or catalytic aerobic conditions. 16 Additionally, under strong basic conditions a retro-[1,3]-silatropic process within ortho -silyl phenols has been well reported.…”

Section: Resultsmentioning

confidence: 99%

Aryne cycloaddition reactions of benzodioxasilines as aryne precursors generated by catalytic reductive ortho-C H silylation of phenols with traceless acetal directing groups

et al. 2017

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Diversely substituted arylsilyl triflates, as aryne precursors for aryne cycloaddition reactions, were accessed from benzodioxasilines. Catalytic reductive C–H ortho-silylation of phenols with traceless acetal directing groups was exploited to prepare benzodioxasilines. Sequential addition of MeLi and then trifluoromethanesulfonic anhydride to benzodioxasilines provided arylsilyl triflates in a single pot. Notably, this approach was successfully utilized to prepare sterically hindered 1,2,3-trisubstituted arylsilyl triflates, which ultimately underwent fluoride-mediated aryne cycloaddition.

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“…Encouraged by this early result we wished to apply the Dötz reaction to the synthesis of heterocyclic systems such as aflatoxin B2 (4) and cryptosporin, which, by necessity would utilize heterosubstituted a,b-unsaturated Fischer carbene complexes in the key benzannulation step, Scheme 3. Somewhat naively we proposed a convergent strategy to the synthesis of aflatoxin B2 (4), a representative member of the furo [2,3-b]benzofuran 9 family of mycotoxins, which was to involve a benzannulation reaction between the carbene complex 5 and the functionalized acetylene 6.…”

Section: Resultsmentioning

confidence: 99%