DDQ,

Selective oxidation of secondary alcohols to ketones is usually performed with CrOj/HjSO, I I in acetone (Jones reagent) or with CrOjPyj (Collin s reagent) in the presence of acid-sensitive groups (H.G. Bosche, 1975 C. Djerassi, 1956 W.S. Allen, 1954). As mentioned above, a,)S-unsaturated secondary alcohols are selectively oxidized by MnOj (D.G. Lee, 1969 D. Arndt, 1975) or by DDQ (D. Walker, 1967 H.H. Stechl, 1975). 

Donor substituents on the vinyl group further enhance reactivity towards electrophilic dienophiles. Equations 8.6 and 8.7 illustrate the use of such functionalized vinylpyrroles in indole synthesis[2,3]. In both of these examples, the use of acetyleneic dienophiles leads to fully aromatic products. Evidently this must occur as the result of oxidation by atmospheric oxygen. With vinylpyrrole 8.6A, adducts were also isolated from dienophiles such as methyl acrylate, dimethyl maleate, dimethyl fumarate, acrolein, acrylonitrile, maleic anhydride, W-methylmaleimide and naphthoquinone. These tetrahydroindole adducts could be aromatized with DDQ, although the overall yields were modest[3]. 

Methyl 1.2,3,4-tetracarbazole-2-acetate Methyl 4-oxo-l,2,3,4-tetraIlyd o-ca ba2oIe-2-acetate DDQ, THF, HjO 85 [5]... 

A solution of methyl l,2,3,4-tetrahydrocarbazoIe-2-acetate (5.94 g) in THF (195ml) containing water (15ml) was cooled to 0"C and DDQ (11.22 g) dissolved in dcoxygenated THF (75 ml) was added. The solution was maintained at 0°C for 2 h and then evaporated in vacuo. The residue was dissolved in EtOAc and washed thoroughly with aq. NaHCOj solution to remove dichlorodicyanohydroquinone. The EtOAc was then dried (MgS04) and evaporated to give methyl 4-oxo-l,2,3,4-tetrahydrocarbazole-2-acetate (5.23 g) in 85% yield. 

Hydrogen Abstra.ction. These important reactions have been carried out using a variety of substrates. In general, the reactions involve the removal of hydrogen either direcdy as a hydrogen atom or indirectly by electron transfer followed by proton transfer. The products are derived from ground-state reactions. For example, chlorarul probably reacts with cycloheptatrienyl radicals to produce ether (50) (39). This chemistry contrasts with the ground-state reaction in which DDQ produces tropyhum quinolate in 91% yield (40). 

Fig. 22. Synthesis of spirorenone [74220-07-8] (156) where DDQ = 2,3-dichloro-5,6dicyano-l,4-ben2oquinone.

Dioxopiperazines are amongst the most ubiquitous of natural products (75FOR(32)57) and they are formally derived by the cyclodimerization of a-amino acids (69CCC4000) or their esters. A number of methods are available for their oxidation to the corresponding pyrazines. Treatment of 2,5-dioxopiperazines with triethyl- or trimethyl-oxonium fluorobor-ate followed by oxidation with DDQ, chloranil or iodine results in pyrazine formation, usually in high yields (Scheme 63) (72JCS(P1)2494). 

To cleave p-methoxyphenylmethyl (MPM) ethers DDQ (dichlorodicy-anobenzoquinone)//-BuOH-CH2Cl2 phosphate buffer (pH 7.0), 4.5 h. 

This order was chosen so that DDQ (dichlorodicyanobenzoquinone) treatment would not oxidize a dep otected allylic alcohol at C.73, and so that the C.47 hemiketal would still be protected (as the ketal) during basic hydrolysis (step 3). 

Several methoxy-substituted benzyl ethers have been prepared and used as protective groups. Their utility lies in the fact that they are more readily cleaved oxidatively than the unsubStituted benzyl ethers. The table below gives the relative rates of cleavage with dichlorodicyanoquinone (DDQ). ... 

Cleavage of MPM, DMPM, and TMPM ethers with DDQ in CHzCIs/HzO at 20 ... 

Dichlorodicyanoquinone (DDQ), CH2CI2, H2O, 40 min, it, 84-93% yield.This method does not cleave simple benzyl ethers. This method was found effective in the presence of a boronate. The following groups are stable to these conditions ketones, epoxides, alkenes, acetonides, to-sylates, MOM ethers, THP ethers, acetates, benzyloxymethyl (BOM) ethers, and TBDMS ethers. 

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. 

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