Quinone monoacetal

The synthetic techniques of in generation of the quinone and utilisation of quinone monoacetals avoid the problems of instability, sequential... 

Quinone monoacetals such as 2-methoxyben2oquinonemonoacetal [64701-03-7] (66) show regiospeciftc addition of active methylene compounds (66), yielding 83% (67) and 63% (68) on reactions with ethyl malonate. 

Quinone dyes, 9 503 Quinone ketals, anodic oxidation of hydroquinone ethers to, 21 264 Quinone methides, 2 209-211 Quinone Michael addition chemistry, 21 248-249, 250, 252 Quinone monoacetals, 21 251 Quinone monoimine (QMI), 19 246 Quinone oximes, formation of,... 

Electron-rich arenes react with quinone monoacetal 194 at the carbon a to the quinone carbonyl group with ring opening of the heterocycle. The reaction was mediated by catalytic amounts of TMSOTf furnishing the aryl addition products in good to excellent yields (53-99%) (Equation 64) <2001CPB1658>. 

Quinone monoacetals. Wheeler et aI.2 have obtained the highest yields reported to date for oxidation of 1,5-naphthalenediol (la) to juglone (2a) by use of TTN in methanol. The yield is improved somewhat by use of TTN supported by Celite for... 

Trimethylsilyl triflate in 3.0m lithium perchlorate-ethyl acetate is an effective promoter of 5 + 2-cycloaddition reactions between quinone monoacetal and 2,3-dimethylbut-2 -ene.2 86... 

Oxidation of Phenol Derivatives to Quinone Monoacetals and Quinones... 

In 1987, Kita and co-workers first developed a general and high yielding (59% quant.) route to p-benzoquinone monoacetals (2a) and spirolactones from para-substituted phenols (la) with PIFA in MeCN in the presence of alcohols (R"OH) [27]. Similar methods for preparing quinone monoacetals and quinol ethers have been developed independently by Lewis et al. (PIDA/CH2C12-R"OH (11-65% yields)) [28] and Pelter et al. (PIDA/R"OH (65-99% yields)) [29] [Eq.(l)]. 

Mild and high yielding oxidation reactions of phenol derivatives to the corresponding quinone monoacetals, quinols, and quinones using PIDA or PIFA [Eqs. (1) - (3)] have been developed independently by Kita et al. [27], Lewis et al. [28], and Pelter et al. [29], and have been utilized extensively for the syntheses of... 

Corey and Wu utilized PIDA oxidation leading to the quinone monoacetal (126) for the initial step of enantioselective total synthesis of miroestrol (4), which is the folk medicine of southeast Asia, isolated from Pueraria mirifica (Thai kwao keur) [86] (Scheme 5). 

The manumycin family were isolated from Streptomyces parvulus (Tii 64) and possess a wide range of biological properties. Taylor and co-workers synthesized manumycin A (7) via the quinone monoacetal (131), which was prepared by PIDA oxidation, followed by epoxidation and alkylation on the cyclohexa-dienone (130) [90] (Scheme 8). Other members of the mamumycin family of antibiotics such as alisamycin, asukamycin, and ( )-nisamycin (8) have been synthesized by similar strategies [91]. 

Similarly, o-alkoxyphenols are converted efficiently to o-quinone monoacetals, which have also been used as the key precursors for natural product synthesis using PIDA or PIFA. 

Transformation of o-methoxyphenol (135) into o-quinone monoacetal (136) using PIDA was used for the initial step of the synthesis of the enediyne aglycone, ( )-calicheamicinone (10), of the potent antitumor agent calicheamicin [93] (Scheme 10). 

In the previous reaction when the solvent was changed to acetonitrile-methanol, quinone monoacetals were formed. Both products were used for the synthesis of 5-oxygenated indoles [11], This type of transformation also occurred using DIB (Section 3.3) however, the use of BTI activated 4-alkyl phenols which reacted not only with methanol but also with other nucleophiles, simple ones such as water and fluoride, or more complex, according to the general scheme ... 

Conjugate addition to quinone monoacetals.2 These substrates undergo only 1,2-addition with (CH3)2CuLi and most Grignard reagents, but 1,4-addition can be achieved by complexation of the acetal with 2 equiv. of 1. 

A radical cyclization onto cross-conjugated quinone monoacetals provides a general approach to 5-hydroxydihy-drobenzoj/ jfurans upon aromatization with />-toluenesulfonic acid (Scheme 99) <2003GC526>. A biomimetic route to dihydrobenzofurans employs a dihydroquinone-mediated reductive cyclization of 2-hydroxyethyl-substituted quinone precursors <2001JOC4965>. 

Quinone monoacetal, which is obtained by careful hydrolysis of quinone diacetal, can also be prepared directly y anodic oxidation under modified reaction conditions. ... 

A more detailed study of this process has sought to establish the scope of the process. Thus Schultz and his coworkers have reported that irradiation of the cyclohexadienone (269) affords the adduct (270). This process can be quantitative using extended photolysis times but if the reaction is stopped after 14 h a 1 1 mixture of (270) and (271) is obtained. Other examples of the process are reported. The irradiation of a series of quinone monoacetals (272) in acetic acid has provided a flexible high yield route to substituted cyclopentenones. Such a rearrangement path is typical of the processes encountered in the photochemical rearrangement of cross conjugated cyclohexadienones. Some examples of the utility of this system are shown in Scheme 9. - ... 

Nagamatsu et al. have shown that liquid crystal and various other media can greatly influence the stereochemistry of uracil photodimerization. Pirrung and Nunn have shown that irradiation of a series of quinone monoacetals (5) in acetic acid provides a flexible high-yield route to substituted cyclopentenones. 

As already shown in Scheme 16, the electrochemically generated /t-quinone monoacetal (84) reacted with 3-cyanophthalide anion 85 to give the anthraquinone 86. Similarly, PhI(OAc)2-promoted oxidation of 4-substituted phenols in MeOH provides the corresponding cyclohexa-2,5-dienones, which react with the anion of 3-cyanophthalide to yield a variety of anthraquinones . A-Acetyltyrosine ethyl ester 456 was subjected to... 

PhI(OAc)2-mediated oxidation in MeOH at ambient temperature for 5 min to afford a mixture of crude dienones, which reacted directly with the phthalide anion to give the corresponding anthraquinone 457 in 62.5% overall yield (Scheme 89). In the case of o-quinone monoacetals , similar results have been obtained. 

MB Hocking, M Ko, and TA Smith. Detection of intermediates and isolation of hydro-quinone monoacetate in the Dakin oxidation of p-hydroxyacetophenone. Can. J. Chem. 56 2646-2649, 1978. 

Epoxidation with Alkylhydroperoxide. The epoxidation of quinone monoacetals in the presence of tritylhydroperoxide using KHMDS was shown to produce the desired epoxides in good yields (eq 47). ... 

A two-step synthesis of highly functionalized isoxazoles 21 has been described via regio- and site-selective 1,3-DC of stable orffeo-disubstituted benzonitrile oxides to ortho-quinone monoacetals followed by dehydrogenation with Ni02 (14CL1607). 

The DA reaction of methacrolein with 1,3-dienol derivatives was catalyzed by BINOL derived titanium complexes, giving the endo adduct with high enantiose-lectivity [155]. The reaction was performed in the absence of MS, since MS can act as an achiral catalyst in this reaction and compromise the product enantiomeric excess. Similarly, the DA reaction of juglone with butadienyl acetate catalyzed by BINOL-Ti complex proceeds in only 9% ee in the presence of MS, whereas the reaction proceeds in 76-96% ee in the absence of MS to provide the endo adducts useful for the synthesis of anthracyclines and tetracycline [155,156). The drawback of the above method is the instability of the addition products, owing to their high tendency to aromatize. Corey improved this DA reaction with quinone monoacetal as a supplant of juglone or benzoquinone [157] (Scheme 14.64). 

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