Synthesis of regiospecifically substituted 2-hydroxybenzocyclobutenones

Lear, Yvonne; Durst, Tony

doi:10.1139/v97-098

Cited by 23 publications

(9 citation statements)

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“…The synthesis starts with readily available bromoaldehyde 2 (Scheme ) obtained by directed ortho ‐metalation of p ‐anisaldehyde3b,5 followed by treatment with CBr 4 . Subsequent condensation of 2 with methyl isocyanoacetate proceeds through the formation of the Schöllkopf 2‐oxazoline6 and provides after workup N ‐formyl dehydroaminoesters 3 as a mixture of two geometrical E / Z isomers.…”

Section: Resultsmentioning

confidence: 99%

An Asymmetric Approach towards (–)‐Aphanorphine and Its Analogues

et al. 2009

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Section: Resultsmentioning

confidence: 99%

An Asymmetric Approach towards (–)‐Aphanorphine and Its Analogues

et al. 2009

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“…The concept was initially validated through the synthesis and cyclization of the macrocyclic ether 11 , which was prepared from aldehyde 6 9 (Scheme ). The exposure of 11 to DDQ under our previously reported conditions3 resulted in a smooth reaction to form tetrahydropyrone 12 in 73 % yield.…”

Section: Methodsmentioning

confidence: 99%

Oxidative Carbocation Formation in Macrocycles: Synthesis of the Neopeltolide Macrocycle

Floreancig

2009

Angew Chem Int Ed

122

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Processes for the functionalization of carbon-hydrogen bonds are the focus of significant attention in organic synthesis [1] in response to the need to streamline molecular assembly. As a continuation of our efforts to generate carbocations through single-electron oxidation reactions, [2] we recently reported[3] DDQ-mediated cyclization reactions of benzylic and allylic ethers (Scheme 1; DDQ =2,3-dichloro-4,5-dicyanoquinone). Keywordscarbocations; C-H activation; macrocycles; natural products; oxidation These reactions proceed through oxidative cleavage of a carbon-hydrogen bond to form oxocarbenium ions that react with appended nucleophiles.[4] The use of relatively inert ethers as precursors to reactive electrophiles is strategically attractive, because facile substrate preparation makes etherification a useful fragment-coupling process for convergent syntheses. Oxidative carbocation generation enables the inclusion of acid-sensitive functional groups in starting materials and products, and provides an opportunity to incorporate multiple precursors to electrophiles in a synthetic intermediate. These electrophiles can later be revealed through the use of chemically orthogonal conditions. [5] Macrocyclic oxocarbenium ions are interesting synthetic intermediates as a result of their capacity to engage in transannular nucleophilic addition reactions. The viability of these intermediates was demonstrated by the Wender research group in the synthesis of bryostatin analogues.[6] Scheidt and co-workers recently reported [7] carbon-carbon bond formation via a macrocyclic oxocarbenium ion formed in a Lewis acid mediated condensation, and related examples followed.[8] However, the generality of this remarkable protocol is not clear: In the absence of conformational preorganization, the process requires the formation of highly reactive intermediates through kinetically unfavorable pathways. A potentially more general approach to the formation of macrocyclic oxocarbenium ions for carbon-hydrogen-bond functionalization is the oxidation of preformed macrocyclic ethers with DDQ (Scheme 2). Herein, we report cyclization reactions that proceed through oxidatively generated macrocyclic oxocarbenium ions (3→4→5) and demonstrate the applicability of the protocol to the construction of complex molecules through a brief formal synthesis of neopeltolide.

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“…Column chromatography was performed on silica gel (Kieselgel 60, 200-400 mesh). 9,9-Dioctyl-9H-fluoren-2amine (3b), [33] 2-bromo-6-hydroxybenzaldehyde (1a), [34] and 2bromo-6-methoxybenzaldehyde (1b) [35] were prepared according to procedures from literature.…”

Section: Generalm Ethodsmentioning

confidence: 99%

How To Reach Intense Luminescence for Compounds Capable of Excited‐State Intramolecular Proton Transfer?

Skonieczny

Yoo

Larsen

et al. 2016

Chemistry A European J

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Photoinduced intramolecular direct arylation allows structurally unique compounds containing phenanthro[9',10':4,5]imidazo[1,2-f]phenanthridine and imidazo[1,2-f]phenanthridine skeletons, which mediate excited-state intramolecular proton transfer (ESIPT), to be efficiently synthesized. The developed polycyclic aromatics demonstrate that the combination of five-membered ring structures with a rigid arrangement between a proton donor and a proton acceptor provides a means for attaining large fluorescence quantum yields, exceeding 0.5, even in protic solvents. Steady-state and time-resolved UV/Vis spectroscopy reveals that, upon photoexcitation, the prepared protic heteroaromatics undergo ESIPT, converting them efficiently into their excited-state keto tautomers, which have lifetimes ranging from about 5 to 10 ns. The rigidity of their structures, which suppresses nonradiative decay pathways, is believed to be the underlying reason for the nanosecond lifetimes of these singlet excited states and the observed high fluorescence quantum yields. Hydrogen bonding with protic solvents does not interfere with the excited-state dynamics and, as a result, there is no difference between the occurrences of ESIPT processes in MeOH versus cyclohexane. Acidic media has a more dramatic effect on suppressing ESIPT by protonating the proton acceptor. As a result, in the presence of an acid, a larger proportion of the fluorescence of ESIPT-capable compounds originates from their enol excited states.

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Synthesis of regiospecifically substituted 2-hydroxybenzocyclobutenones

Cited by 23 publications

References 0 publications

An Asymmetric Approach towards (–)‐Aphanorphine and Its Analogues

An Asymmetric Approach towards (–)‐Aphanorphine and Its Analogues

Oxidative Carbocation Formation in Macrocycles: Synthesis of the Neopeltolide Macrocycle

How To Reach Intense Luminescence for Compounds Capable of Excited‐State Intramolecular Proton Transfer?

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