Quinones monoketals

Omura, K. Iodine oxidation of alpha -tocopherol and its model compound in alkaline methanol unexpected isomerization of the product quinone monoketals. J. Org. Chem. 1989, 54, 1987-1990. 

Porco s route to (—)-kinamycin C (3) began with 2,5-dihydroxybenzaldehyde (38), which was elaborated to the enone 35 by the sequence shown in Scheme 3.6. Regioselective bromination [25] followed by methylation and reduction of the aldehyde function afforded the primary alcohol 39. The alcohol 39 was dearomatized by treatment with bis(acetoxy)iodobenzene, to afford the quinone monoketal 41. Transketalization with 1,3-propanediol followed by silylation of the primary alcohol generated the silyl ether 42 in 72 % yield over three steps. 

Addition to quinone monoketals and quinol ethers.2 Complexation of quinone monoketals or quinol ethers with MAD permits 1,4-addition of organo-lithium and Grignard reagents. Highest yields obtain with aryl, vinyl, and acetylenic organometallics. 

Oxidative Conversion of Arenols into ortfio-Quinols and ortfio-Quinone Monoketals - A Useful Tactic in Organic Synthesis... 

The oxidative activation of arenes is a powerful and versatile synthetic tactic that enables dearomatization to give useful synthons. Central to this chemistry are hydroxylated arenes or arenols, the phenolic functions of which can be exploited to facilitate the dearomatizing process by two-electron oxidation. Suitably substituted arenols can hence be converted, with the help of oxygen- or carbon-based nucleophiles, into ortho-quinone monoketals and ortho-quinols. These 6-oxocyclohexa-2,4-dienones are ideally functionalized for the construction of many complex and polyoxygenated natural product architectures. Today, the inherent and multiple reactivity of arenol-derived ortho-quinone monoketals and ortho-quinols species is finding numerous and, in many cases, biomimetic applications in modern organic synthesis. 

I 75 Oxidative Conversion ofArenols into ortho-Quinols and ortho-Quinone Monoketals... 

Many other metals have been used over the years to generate ortbo-quinone monoketals and ortbo-quinol derivatives [6], but the venerable Wessely oxidation remains to this day the most commonly used metal-based method. For the generation of ortbo-quinols by selec-... 

The ability of the cydohexa-2,4-dienone unit of ortbo-quinone monoketals and other ortho-quinol derivatives to react as either a diene or a dienophile component in [An+2n cydoadditions is arguably their prindpal virtue in organic synthesis, and paradoxically it is also the prindpal reason why it is often difficult to exploit them in synthesis they often dimerize faster than they can combine with another -system partner. Adler, Andersson, and coworkers have extensively studied the behavior of ortbo-quinols in Diels-Alder cydoadditions,... 

Here again, the cycloaddition is endo-selective, with only regioisomers 79 being formed, and, when using 2- and/or 3-substituted furans, only the unsubstituted furan double-bond reacts in these inverse electron-demand Diels-Alder processes [134-136]. Indoles, pyrroles, and thiophenes can also be made to react as dienophiles with ortho-quinone monoketals... 

Liao and Wei took advantage of the possibility of photochemically rearranging cyclohexa-2,4-dienones into bicyclo[3.1.0]hexenones in their approach to synthetically useful cyclo-pentenones such as 135 [6, 160-162]. This approach was based on the acid-catalyzed cyclopropane ring-opening of bicyclo[3.1.0]hexenones such as 134, as generated photochemically from non-dimerizing ortfio-quinone monoketals such as 133 (Figure 33) [165]. 

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