Dichlorodicyanobenzoquinone DDQ

The first successful transformation of protoberberines to benzo[c]-phenanthridines was reported by Onda et al. (122,123). Irradiation of the enamines 200 and 195, the Hofmann degradation products of the corresponding protoberberines, in benzene afforded the initial photoproducts 201, which immediately rearranged to the tetrahydrobenzo[c]phenanthridines 202 in 70% yield (Scheme 37). Dehydrogenation of 202 afforded dihydro-chelerythrine (203) and dihydrosanguinarine (204), which were further oxidized with dichlorodicyanobenzoquinone (DDQ) to yield chelerythrine (205) and sanguinarine (206), respectively. 

Donor/acceptor association and the electron-transfer paradigm form the unifying theme for the C—C bond cleavage of various benzpinacols and diary-lethane-like donors in the presence of different electron acceptors (such as chloranil (CA), dichlorodicyanobenzoquinone (DDQ), tetracyanobenzene (TCNB), triphenylpyrylium (TPP+), methyl viologen, nitrosonium cation, etc.). Scheme 13 reminds us how this is achieved by either CT photolysis of the D/A pair or via diffusional quenching of the excited electron acceptor A by the electron donor D. 

New applications of dichlorodicyanobenzoquinone (DDQ) for the dehydrogenation of ketones include the conversion of a 4,7-dien-3-one into the 4,6,8(14)-trienone, which is further dehydrogenated to the l,4,6,8(14)-tetraenone with acidic catalysis.The dehydrogenation of a 4-en-6-one with DDQ affords the 2,4-dien-6-one. Selective 1,2-dehydrogenation of 5a-cholestan-3-one has been achieved with palladium acetylacetonate and oxygen.Possible alternative mechanisms are discussed. 

Sammes and co-workers (314) have also shown that some piperazine-2,5-diones (89) react with an excess of triethyloxonium iluoroborate to give a mixture of cis-and rra/is-2,5-diethoxy-3,6-dihydropyrazines (90) which can be oxidized with dichlorodicyanobenzoquinone (DDQ) to 2,5-diethoxypyrazines (91) in high yield. Many similar oxidations of dihydropyrazines have recently been described (314a). 

A recent paper reports the oxidation of benzylic a-hydroxyphosphonates to aroylphos-phonates in good yields, by refluxing them with 10 equiv. of Mn02 in toluene The same paper reports that other oxidizing agents, including pyridinum chlorochromate and dichlorodicyanobenzoquinone (DDQ),or the Swem method are also applicable for the oxidation of benzylic a-hydroxyphosphonates to benzoylphosphonates. This approach to acylphosphonates was found, however, to be limited to tert-huty esters. ... 

The silylenol ether formed from (47) and trimethylchlorosilane was cyclized in situ, and the reaction mixture was worked up under acidic conditions to give the ketone (558). This was subjected to reduction with sodium borohydride, acid-catalyzed elimination of water, and oxidation with dichlorodicyanobenzoquinone (DDQ) to give the bicyclic ester (560). Introduction of a methoxy substituent into the retinoid structure (560) was likewise effected via the ketone (558). When this ketone was ketalized with methyl o-formate, methanol was eliminated and the product was oxidized, its six-membered ring system undergoing aromatization to form a substituted phenyl group. 

Trityl tetrafluoroborate oxidizes secondary alcohols to ketones primary, secondary diols are selectively oxidized at the secondary position by this reagent. /Lt-Oxo-bis(chlorotriphenylbismuth) is a mild reagent for the oxidation of alcohols, and is particularly suitable for the oxidation of the hydroxy-group in allylic alcohols. Dichlorodicyanobenzoquinone (DDQ) with periodic acid in HCl-benzene has also been used for the latter purpose. ... 

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