Orthoquinone Monoketals Research Articles

Total Synthesis of Macaranin B.

This study describes the total synthesis of macaranin B, a naturally occurring ellagitannin containing 1-O-galloyl and 3,6-O-macaranoyl groups in an axial-rich d-glucose. The key steps of the synthesis include an oxidative coupling reaction of galloyl groups with 1,2,4-orthoacetylglucose moiety and oxa-Michael addition/elimination using an orthoquinone monoketal. This facilitates the construction of the macaranoyl group and the first total synthesis of macaranin B.

ChemInform Abstract: Diels—Alder Cycloadditions of Masked o‐Benzoquinones with Alkenes.

AbstractDiels—Alder cycloaddition of oxobutenylated orthoquinone monoketals, generated in situ, with olefinic dienophiles yields bicyclo[2.2.2]octenones with high regio‐ and stereoselectivity.

Diels-Alder Cycloadditions of Masked o-Benzoquinones with Alkenes.

Diels-Alder cycloadditions of 3-oxobut-1-enyl substituted orthoquinone monoketals with olefinic dienophiles furnished functionalized ortho-endo bicyclo[2.2.2]octenone derivatives with high regio- and stereoselectivities. The competition between self-dimerization and Diels-Alder cycloaddition with an external dienophile usually exists, except in the case of 5-substituted orthoquinone monoketal.

A unified strategy for the synthesis of highly oxygenated diaryl ethers featured in ellagitannins

Ellagitannins are a family of polyphenols containing more than 1,000 natural products. Nearly 40% of these compounds contain a highly oxygenated diaryl ether that is one of the most critical elements to their structural diversity. Here, we report a unified strategy for the synthesis of highly oxygenated diaryl ethers featured in ellagitannins. The strategy involves oxa-Michael addition of phenols to an orthoquinone building block, with subsequent elimination and reductive aromatization. The design of the building block--a halogenated orthoquinone monoketal of gallal--reduces the usual instability of orthoquinone and controls addition/elimination. Reductive aromatization is achieved with perfect chemoselectivity in the presence of other reducible functional groups. This strategy enables the synthesis of different diaryl ethers. The first total synthesis of a natural ellagitannin bearing a diaryl ethers is performed to demonstrate that the strategy increases the number of synthetically available ellagitannins.

Total Synthesis of (−)-Anisatin

A novel synthetic route to (-)-anisatin has been developed. Our synthesis features a rhodium-catalyzed 1,4-addition of an arylboronic acid, an intramolecular Diels-Alder reaction of an ortho-quinone monoketal, a stereoselective [2,3]-Wittig rearrangement, and construction of the oxabicyclo [3.3.1] skeleton via cleavage of an epoxide by a primary amide.

ChemInform Abstract: Highly Diastereoselective Synthesis of Orthoquinone Monoketals Through λ3‐Iodane‐Mediated Oxidative Dearomatization of Phenols.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Highly Diastereoselective Synthesis of Orthoquinone Monoketals through λ3‐Iodane‐Mediated Oxidative Dearomatization of Phenols

Highly Diastereoselective Synthesis of Orthoquinone Monoketals through λ³‐Iodane‐Mediated Oxidative Dearomatization of Phenols

Highly Diastereoselective Synthesis of Orthoquinone Monoketals through λ3‐Iodane‐Mediated Oxidative Dearomatization of Phenols

Highly Diastereoselective Synthesis of Orthoquinone Monoketals through λ³‐Iodane‐Mediated Oxidative Dearomatization of Phenols

Regio- and stereoselectivities in Diels–Alder cyclodimerizations of orthoquinonoid cyclohexa-2,4-dienones

The [4+2] cyclodimerization of cyclohexa-2,4-dienone derivatives of the orthoquinone monoketal and orthoquinol types has been the topic of numerous investigations over the last 50 years in the aim of rationalizing the extraordinary level of regio-, site-, and stereoselectivities observed in these processes. In particular, the double diastereo-π-facial differentiation expressed in cyclodimerizations of chiral orthoquinols (i.e., 6-alkyl-6-hydroxycyclohexa-2,4-dienones) is an important aspect of these transformations, for they relate to the construction of several natural products. The experimental and theoretical results that are described in this article offer a comprehensive understanding of the factors controlling these site-specific regio- and diastereoselectivities. Our interpretation of these results relies on a combination of Woodward–Hoffmann and Salem–Houk secondary orbital interactions and Cieplak-type hyperconjugative effects in bispericyclic C 2-symmetric transition states.

First Asymmetric Synthesis of Orthoquinone Monoketals via Anodic Oxidation of 2-Alkoxyphenol Ethers

not Available.

Electrochemical Synthesis of Dimerizing and Nondimerizing Orthoquinone Monoketals.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Electrochemical Synthesis of Dimerizing and Nondimerizing Orthoquinone Monoketals

Anodic oxidation of appropriately substituted 2-methoxyphenols or alpha-(2-methoxyphenoxy)-2-methylpropionic acids in the presence of methanol furnishes stable orthoquinone monoketals, and thus constitutes a valuable alternative to the use of chemical oxidants that are often based on toxic metallic species. The propionic acid derivatives are initially converted into O-spirolactonic quinone bisketals that are then selectively hydrolyzed into the desired monoketal compounds. In the absence of blocking substituents, orthoquinone monoketals spontaneously undergo Diels-Alder dimerizations into tricyclododecadienedienones with extraordinary site selectivity, regioselectivity, and stereoselectivity. Suggestions are made to open up a new track for a long awaited rationalization of these controls on the basis of the intramolecular [2 + 2] reactivity of these orthoquinone monoketal-derived cyclodimers.

First Asymmetric Synthesis of Orthoquinone Monoketal Enantiomers via Anodic Oxidation

An asymmetric synthesis of orthoquinone monoketals was accomplished using anodic oxidation to convert aryl methyl ethers bearing a chiral ethanol unit into orthoquinone bisketals, followed by monohydrolysis of their dimethyl ketal unit. All four possible stereoisomers were generated in a diastereoselective manner by varying the attachment point of the chiral pro-ketal alcoholic auxiliary to the starting arene. A preliminary screening of subsequent nucleophilic addition reactions confirmed the potential utility of these synthons in asymmetric synthesis. [reaction: see text]

Regiospecific synthesis of a benanomicinone/pradimicinone analogue.

[reaction: see text] Condensation of a phenylsulfinyl naphthoate with an ortho-quinone monoketal has been used to accomplish a total synthesis of a benanomicinone/pradimicinone analogue.

Total synthesis of (+/-)-O-methyl PD 116740.

[reaction: see text] Condensation of the phthalide sulfide with an ortho-quinone monoketal was employed as a key step in the first total synthesis of a derivative of (+/-)-PD 116740.

Orthoquinone monoketal chemistry. Experimental and density functional theory studies on orthoquinol acetate rearrangements

The non-dimerizing orthoquinone monoketal, 6-acetoxy-6-methoxy-3-methoxycarbonylcyclohexa-2,4-dienone, conveniently prepared from oxidative acetoxylation of its parent phenol with PhI(OAc) 2 in CH 2Cl 2AcOH (3:1), cleanly undergoes 1,3-acetoxy migrations in the presence of silica gel at room temperature to furnish a 60:40 product mixture conceivably derived from [3,5] and [3,3] sigmatropic rearrangements. Density functional theory calculations indicate that the [3,5] shift is pseudopericyclic, has a remarkably low activation energy of 20.1 kcal/mol, and is favored by 5.4 kcal/mol over the pericyclic [3,3] shift, in qualitative agreement with the experimental observations.

Cyclization Pathways of a (Z)-Stilbene-Derived Bis(orthoquinone monoketal)

Lead tetraacetate mediated oxidation of a (Z)-bisphenolic stilbene derivative affords a bis(orthoquinone monoketal) product. Thermolysis studies of this highly unsaturated dione reveal that sigmatropic hydrogen shifts, followed by either of two distinct solvolytic ring closures, constitute the predominate reaction pathways under heating. No evidence for a desired 6π electron electrocyclization was forthcoming.