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Completing the Redox-Series of Silicon Trisdioxolene: ortho-Quinone and Lewis Superacid Make a Powerful Redox Catalyst.

ABSTRACT: Quinones are mild oxidants, the redox potentials of which can be increased by supramolecular interactions. Whereas this goal has been achieved by hydrogen bonding or molecular encapsulation, a Lewis acid-binding strategy for redox amplification of quinones is unexplored. Herein, the redox chemistry of silicon tris(perchloro)dioxolene 1 was studied, which is the formal adduct of ortho-perchloroquinone Q^Cl with the Lewis superacid bis(perchlorocatecholato)silane 2. By isolating the anionic monoradical 1^.- , the redox-series of a century-old class of compounds was completed. Cyclic voltammetry measurements revealed that the redox potential in 1 was shifted by more than 1?V into the anodic direction compared to Q^Cl , reaching that of "magic blue" or NO⁺ . It allowed oxidation of challenging substrates such as aromatic hydrocarbons and could be applied as an efficient redox catalyst. Remarkably, this powerful reagent formed in situ by combining the two commercially available precursors SiI₄ and Q^Cl .

SUBMITTER: Maskey R

PROVIDER: S-EPMC7839739 | biostudies-literature | 2020 Dec

REPOSITORIES: biostudies-literature

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Completing the Redox-Series of Silicon Trisdioxolene: ortho-Quinone and Lewis Superacid Make a Powerful Redox Catalyst.

Maskey Rezisha R Bendel Christoph C Malzacher Jonas J Greb Lutz L

Chemistry (Weinheim an der Bergstrasse, Germany) 20201124 72

Quinones are mild oxidants, the redox potentials of which can be increased by supramolecular interactions. Whereas this goal has been achieved by hydrogen bonding or molecular encapsulation, a Lewis acid-binding strategy for redox amplification of quinones is unexplored. Herein, the redox chemistry of silicon tris(perchloro)dioxolene 1 was studied, which is the formal adduct of ortho-perchloroquinone Q<sup>Cl</sup> with the Lewis superacid bis(perchlorocatecholato)silane 2. By isolating the anio ...[more]

PMID: 33108014

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Project description:CONSPECTUS: An ortho-quinone methide (o-QM) is a highly reactive chemical motif harnessed by nature for a variety of purposes. Given its extraordinary reactivity and biological importance, it is surprising how few applications within organic synthesis exist. We speculate that their widespread use has been slowed by the complications that surround the preparation of their precursors, the harsh generation methods, and the omission of this stratagem from computer databases due to its ephemeral nature. About a decade ago, we discovered a mild anionic triggering procedure to generate transitory o-QMs at low temperature from readily available salicylaldehydes, particularly OBoc derivatives. This novel reaction cascade included both the o-QM formation and the subsequent consumption reaction. The overall transformation was initiated by the addition of the organometallic reagent, usually a Grignard reagent, which resulted in the formation of a benzyloxy alkoxide. Boc migration from the neighboring phenol produced a magnesium phenoxide that we supposed underwent ?-elimination of the transferred Boc residue to form an o-QM for immediate further reactions. Moreover, the cascade proved controllable through careful manipulation of metallic and temperature levers so that it could be paused, stopped, or restarted at various intermediates and stages. This new level of domestication enabled us to deploy o-QMs for the first time in a range of applications including diastereocontrolled reactions. This sequence ultimately could be performed in either multipot or single pot processes. The subsequent reaction of the fleeting o-QM intermediates included the 1,4-conjugate additions that led to unbranched or branched ortho-alkyl substituted phenols and Diels-Alder reactions that provided 4-unsubstituted or 4-substituted benzopyrans and chroman ketals. The latter cycloadducts were obtained for the first time with outstanding diastereocontrol. In addition, the steric effects of the newly created stereocenters in subsequent reactions of chroman ketals and acetals were studied and proved predictable. Through the use of a chiral auxiliary, Diels-Alder products were deployed in numerous enantioselective reactions including several complex natural products syntheses. In this Account, we summarize our efforts, which we hope have contributed to the synthetic renaissance for this venerable species.

Dataset Information

Completing the Redox-Series of Silicon Trisdioxolene: ortho-Quinone and Lewis Superacid Make a Powerful Redox Catalyst.

Publications

Completing the Redox-Series of Silicon Trisdioxolene: ortho-Quinone and Lewis Superacid Make a Powerful Redox Catalyst.

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