Reaction with DDQ

Ph3C BF, CH2CI2 or CH3CN, H2O. In this case the reaction with DDQ failed to go to completion. This was attributed to the reduced electron density on the aromatic ring because of its attachment at the more electron-poor anomeric center. 

The reaction with valerolactam 24 was also investigated, with surprising results. The reaction with BSTFA gave the silyl lactam 78 rather than the silyl imidate 25, as shown in Scheme 3.33. Subsequent reaction with DDQ gave a C-N adduct 79... 

In the early 1990s, FTIR was being evaluated at Merck for the in situ monitoring of reactions. This new technology was expected to provide a powerful means to study a reaction as well as a method for analytical control in production [28]. Both silyl imidate formation and the reaction with DDQ could be conveniently monitored by FTIR, as shown in Figure 3.13. Silyl imidate formation was indicated by the appearance of an absorbance at 1667.5 cm4 with concomitant disappearance of the absorbance corresponding to BSTFA at 1324.0cm-1. A new absorbance... 

Figure 3.15 FTIR monitoring of the reaction with DDQ. Reprinted with permission from [28], copyright Merck Co., Inc., Whitehouse Station, NJ.

DDQ ( red = 0.52 V). It is noteworthy that the strong medium effects (i.e., solvent polarity and added -Bu4N+PFproduct distribution (in Scheme 5) are observed both in thermal reaction with DDQ and photochemical reaction with chloranil. Moreover, the photochemical efficiencies for dehydro-silylation and oxidative addition in Scheme 5 are completely independent of the reaction media - as confirmed by the similar quantum yields (d> = 0.85 for the disappearance of cyclohexanone enol silyl ether) in nonpolar dichloromethane (with and without added salt) and in highly polar acetonitrile. Such observations strongly suggest the similarity of the reactive intermediates in thermal and photochemical transformation of the [ESE, quinone] complex despite changes in the reaction media. 

A number of compounds react rapidly with DDQ at room temperature. They include allylic and benzylic alcohols, which can thus be selectively oxidized, and enols and phenols, which undergo coupling reactions or dehydrogenation, depending on their structure. Rapid reaction with DDQ is also often observed in compounds containing activated tertiary hydrogen atoms. The workup described here can be used in all these cases. 

The diketoester 192 reacts with substituted hydrazines to produce tetrahydrobenzodipyrazoles in high yields which are converted into dihydrobenzodipyrazoles on reaction with DDQ in refluxing dioxane (Equation 127) <2005BML1315>. 

PMB ethers can be cleaved oxidatively with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)11 in dichloromethane/water tor with cerium ammonium nitrate (CAN) in acetonitrile/water.12 Many other protecting groups such as esters, isopropylidene acetals, benzyl ethers, allyl ethers and f-butyldiphenyl silyl (TBDMS) ethers are stable to these conditions (Scheme 2.4). The cleavage reaction, with DDQ is initiated with a single-... 

Introduction. Quinones of high oxidation potential are powerful oxidants which perform a large number of useful reactions under relatively mild conditions. Within this class, DDQ represents one of the more versatile reagents since it combines high oxidant ability with relative stabUity (see also Chloranil). Reactions with DDQ may be carried out in inert solvents such as benzene, toluene, dioxane, THF, or AcOH, but dioxane and hydrocarbon solvents are often preferred because of the low solubility of the hydroquinone byproduct. Since DDQ decomposes with the formation of hydrogen cyanide in the presence of water, most reactions with this reagent should be carried out under anhydrous conditions. ... 

The oxidative dimerization of phenol 22.1 was simulated in vitro. Exposure of this compound to the complex Cu(NO 3) 2-pyridine gave rise to dimers 23.10 and 23.11 by a C-C coupling reaction. Compound 23.11 could be cyclodehydrogenated to 23.10 by reaction with DDQ. On the other hand, exposure of phenol 22.1 to K3Fe(CN)6 gave the product (22.3) of a C-0 coupling, which was then transformed into 23.12 by DDQ cyclodehydrogenation 140) (Scheme 9). 

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