Rapid Syntheses of Benzopyrans from <i>o</i>-OBOC Salicylaldehydes and Salicyl alcohols:  A Three-Component Reaction

Jones, Ryan M.; Selenski, C.; Pettus, Thomas R. R.

doi:10.1021/jo020224v

Cited by 56 publications

(19 citation statements)

References 13 publications

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“…Electron-rich 2π dienophiles, including styrenes, enol ethers, furans, enamines, and imines, underwent this cycloaddition to produce the desired chromans 75 – 86 with >20:1 diastereoselectivity, unless noted otherwise (Table 5 ). 41 β-Substituted o -QMs appear less reactive than their β-unsubstituted counterparts, particularly in regards to their reactions with less polarized olefins. For example, the benzopyran 75 was isolated in a paltry 27% yield and 6:1 dr compared with the 50% yield for its analog 60 .…”

Section: Benzopyrans and Chroman Ketals From O -Qmmentioning

confidence: 96%

“…While aliphatic alkenes proved unreactive, styrene merged with our o -QM to give benzopyran 60 in 50% yield. 41 More electron-rich alkenes gave improved yields. For example, 1-( tert -butoxy)-4-vinylbenzene afforded the corresponding tert -butoxy analog 60 in 80% yield.…”

Section: Benzopyrans and Chroman Ketals From O -Qmmentioning

confidence: 99%

“…For example, 1-( tert -butoxy)-4-vinylbenzene afforded the corresponding tert -butoxy analog 60 in 80% yield. 41 The benzopyran 61 , arising from the troublesome salicylalcohol core (Scheme 1 , inset), was obtained in 45% yield by a modified single-pot protocol, whereby the reduction of the preceding salicylaldehyde was achieved with LAH in the presence of 1-( tert -butoxy)-4-vinylbenzene and followed by the addition of MgBr 2 . 42 This benzopyran was subsequently oxidized to a flavone and its protecting residues were concurrently cleaved by treatment with ZnBr 2 .…”

Section: Benzopyrans and Chroman Ketals From O -Qmmentioning

confidence: 99%

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The Domestication of ortho-Quinone Methides

et al. 2014

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ConspectusAn 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 β-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.

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Section: Benzopyrans and Chroman Ketals From O -Qmmentioning

confidence: 96%

Section: Benzopyrans and Chroman Ketals From O -Qmmentioning

confidence: 99%

Section: Benzopyrans and Chroman Ketals From O -Qmmentioning

confidence: 99%

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The Domestication of ortho-Quinone Methides

et al. 2014

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“…* For correspondence Many efforts have recently been undertaken by the preparation of various pyran derivatives with the aim of obtaining more biologically potent heterocyclic systems. [17][18][19][20][21][22] However, to the best of our knowledge, synthesis of 5-amino-7-aryl-6-cyano-4H -pyrano [3,2b]pyrrole derivatives has never been communicated up to now. In this study, in continuation of our interest in MCRs, 23,24 the one-pot synthesis of 5-amino-7-aryl-6cyano-4H -pyrano[3,2-b]pyrroles by cyclocondensation reaction of 3-hydroxypyrrole, substituted benzaldehydes and malononitrile in the presence of ferric hydrogensulphate, Fe(HSO 4 ) 3 , is described here (figure 1).…”

Section: Introductionmentioning

confidence: 99%

A novel and facile approach for synthesis of 5-amino-7-aryl-6-cyano-4H-pyrano[3,2-b]pyrroles

Sandaroos

Damavandi

2012

J Chem Sci

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“…Building upon our past experiences, we supposed that an imine would engage an o -QM via its lone pair of electrons in a 1,4-conjugate addition, followed by an intramolecular cyclization of the developing phenoxide zwitterion onto the resulting iminium species. This sequence should provide an assortment of N-substituted 3,4-dihydro-2 H -1,3-benzoxazines in a single pot in a manner that is more straightforward than that possible with other processes (Scheme ).…”

mentioning

confidence: 99%