Oxidants 2,3-dichloro-5,6-dicyanobenzoquinone

Oppenauer oxidation, 236 Oxidation of allylic alcohols with dichloro-dicyanobenzoquinone, 248 Oxidation of allylic alcohols with manganese dioxide, 247... 

A two-step transformation of conjugated dienes into non-conjugated ones was proposed for the synthesis of the difficult to-obtain lapachol (355) (a member of a class of antimalarial agents having an activity against the Walker carcinosarcoma 256) from the more available isolapachol 352183. This method consists in an oxidative cyclization of isolapachol 352 by 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) to form a mixture of the products 353 and 354 (equation 127). Treatment of this mixture with dilute acid in... 

The Jones reagent851 and < rt-BuOOH in the presence of chromium(VI) complexes852,853 were found to be particularly useful in the oxidation of tetralins and indans. Oxidation with 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) occurs with an exceptional mechanism.854 In contrast with the radical processes observed in other oxidations DDQ generates a carbocation by hydride abstraction that is trapped by water to form an alcohol ... 

Catalytic hydrogenation of porphyrazines or their Mg complexes with palladium black gives tetrahydrogenated compounds which are oxidized back to the starting materials by a stoichiometric amount of 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ).2 The royal blue products are degraded to cw-succinimide and maleimide, and considered to be the tetraaza analogues of either bacterio-chlorins or isobacteriochlorins. Photochemical reduction of monoazaporphyrins is reported to occur at the meso positions. 

Reaction of the 3-substituted l,2,3-triazolo[4,5-d]pyrimidines (183) with one equivalent of a Grignard reagent in THF afforded the dihydro compounds 185 after hydrolysis of the intermediates 184. Aromatization of 185 by oxidation with potassium ferricyanide (79CPB3176) or with 2,3-dichloro-4,5-dicyanobenzoquinone (DDQ) (89CPB1731) gave the 3-substituted 7-alkyltriazolopyrimidines 186. Replacement of the methylsul-... 

Furthermore, cyclopentenedione (62) reacts with 1,3-dithiolylium tetrafluoroborate (1) in aqueous ethanol with formation of compound (63) which can be easily oxidized using 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) to produce the dithiafulvalene derivative (64) (77CL77). 

Catalytic hydrogenation of the diene (96), from mercuric acetate oxidation of betulin diacetate, yielded (97) and (98). The latter was further reduced to the 18/3H,19/8-lupane (99).70 Isomerization of betulin diacetate with hydrobromic acid in acetic acid-acetic anhydride afforded (97), instead of the usual products with ring E enlarged.71 Glochidone (100) is readily prepared from lupen-3-one by oxidation with 2,3-dichloro-5,6-dicyanobenzoquinone.72 73... 

Since hot pepper is important for the food and the pharmaceutical industries, a range of different methods have been developed for the analysis of capsaicinoids in plant material and finished products. The separation of CPS (la) and nonivamide (11) is especially challenging, since these compounds have similar behavior in many chromatographic conditions. Since synthetic nonivamide is the most common adulterant of capsicum oleoresin, various strategies have been suggested to overcome this problem. Capillary GC does not require previous derivatization of capsaicinoids, but its separatory power seems lower than that of HPLC, currently the most popular technique for the quantization of capsaicinoids. GC is, however, the method of choice for the analysis of the acyl moieties of capsaicinoids as methyl esters. These can be directly produced from capsaicinoids by oxidative N-dealkylation with DDQ (2,3-dichloro-5,6-dicyanobenzoquinone), followed by alcoholysis of the resulting amides with methanol in the presence of an acidic resin (Scheme 4.4) [41]. 

ALLYLIC OXIDATION f-Butyl hydroperox-ide-Chromium carbonyl. 2,3-Dichloro-5,6-dicyanobenzoquinone. 

Whereas empirical force-field calculations predict a ring A boat conformation for lanost-8-en-3-one, combined empirical force-field-extended Hiickel molecular orbital calculations favour a ring A chair conformation. Europium-shift n.m.r. results indicate that the molecule adopts the latter conformation. Studies on the peracetic acid-boron trifluoride etherate Baeyer-Villiger oxidation of 4,4-dimethyl-3-keto-triterpenoids to 5-lactones (18) and their subsequent ring contraction to y-lactones have been reported. Dehydrogenation of lanost-8-en-3j8-ol with 2,3-dichloro-5,6-dicyanobenzoquinone afforded, in addition to the corresponding 7,9(1 l)-diene, the aromatic seco-lanostane derivatives (19)... 

Allylic alcohols are more easily oxidised than saturated alcohols and in this case rates are greatest for the equatorial isomers [42]. Activated manganese dioxide is commonly used for selective oxidations of allylic alcohols, although it will also attack saturated alcohols slowly under special conditions [44]. Its mechanism of action is not understood, although some relevant observations have been reported [43]. 2,3-Dichloro-5,6 dicyanobenzoquinone (DDQ) is a very mild and selective oxidant for allylic alcohols [43]. Kinetic studies [46] on 3a- and 3 9 hydroxy-A -systems (8) revealed a higher rate of oxidation of the pseudo-equatorial 3 -alcohol K jK a = 6), and a large primary isotope effect Kj)IKb ca. 1/5) when the C(3) H was replaced by deuterium. These results indicate a rate-determining hydride abstraction from C(3>, with preferred removal of the pseudo-axial 3C1-H as a result of optimum a-7i overlap in the transition state (9). However, a detailed analysis of thermodynamic parameters shows that the cause of the rate difference appears mainly in the term (A5 ) rep-... 

Three independent syntheses of fukinone (335) have been published. In the first of these, Piers and Smillie ° converted the octalone (336), which they had previously used in connection with their synthesis of aristolone, into (337) by treatment with ethyl formate followed by catalytic reduction. Dehydrogenation of (337) with 2,3-dichloro-5,6-dicyanobenzoquinone and subsequent oxidation and esterification yielded (338). This keto-ester was converted into fukinone (335) by hydrogenation followed by methylation of the enolate ester and dehydration of the resultant keto-alcohol (339). Torrence and Finder have also completed the synthesis of fukinone using the octalone (336) as the key intermediate. 

Nakajima, N., Tanaka, T, Hamada, T, Oikawa, Y, and Yonemitsu, O., Highly stereoselective total synthesis of pikronolide, the aglicon of the first macrolide antibiotic pikromycin. Crucial role of benzyl-type protecting groups removable by 2,4-dichloro-5,6-dicyanobenzoquinone oxidation, Chem. Pharm. Bull., 35, 2228, 1987. 

Dihydropyrimido[4,5-t/]pyridazines 1 (accessible by the reaction of pyrimido[4,5-z/]-pyridazines with organometallic compounds62 or by the photochemical addition of alcohols 63 see Section 7.4.6.2.) are oxidized to the fully conjugated pyrimido[4,5-<7]pyndazine system 2 by 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) or potassium hexacyanoferrate(III).61... 

Further studies are reported on the dehydrogenation of oestrogen derivatives (228)—(230) with 2.3-dichloro-5.6-dicyanobenzoquinone. The initial product, the 9(ll)-dehydro-derivative, is usually oxidized further to give the 9(11)-en-12-one in rather low yield. The 17 -hydroxy-compounds (228) and (229)... 

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