Reactions with p-benzoquinones

A proof for the formation of alkyl radicals was found by their addition to the aci-nitromethane anion (CH2=N02 ) and by their reaction with p-benzoquinone to give the optically active nitroalkane radical-anion and the semiquinone radicals, respectively. In the case of di-r-butyl sulfoxide the f-butyl radical was observed directly by its absorption spectra. 

Scheme 2.7). The phenols were formed during isolation (chromatography on silica gel) from the corresponding cycloadducts. In the reaction with p-benzoquinone, a product was unexpectedly obtained from a hetero-T>ie s-Alder reaction with the quinone acting as a carbonyl dienophile. 

Reaction with p-benzoquinones.6 Fischer and Henderson have found conditions that result in 1,2-addition of various RLi reagents to p-benzoquinonc. The reaction when conducted in ether at —78° results in 4-alkyl-4-hydroxycyclohexa-2,5-diene-l-ones. These products undergo further 1,2-addition with RLi in THF to give dialkyl-cyclohexa-2,5-diene-l,4-diols. Mixed dienediols can be obtained by use of two different RLi reagents. 

Detailed preparation from LiCN (from LiH and acetone cyanohydrin) and TMSC1, followed by its reaction with p-benzoquinone in the presence of 18-Crown-6 and KCN. 

Cadogan et al. [27] reported the DTHDA cycloaddition of parent cross-conjugated carbotriene ([3]dendralene) 106 with some representative electron-withdrawing dienophiles including heterodienophiles (Scheme 2.16). They applied a flash vacuum pyrolysis technique to synthesize parent carbotriene 106 in pure form from 3-vinyl-3-sulfolene. The initial DA reaction with p-benzoquinone (PBQ) at 40 °C afforded mono-adduct 107 (90%), followed by the second HDA reaction with Ph-TAD at 40 °C to provide the mixed bis-adduct 108 (63%). Triene 106 gave mono-adduct 109 in the presence of even an excess amount of TCNE at 40 °C. Ph-TAD was able to react with mono-adduct 109 at 40°C to provide crossed bis-adduct 110 (63%). Bis-adduct 111 was directly obtained (21%) by reaction of 106 with excess Ph-TAD at 40 °C, as same as the reaction with Ph-MI. 

The reaction of o-diphenylcyclobutadiene (generated in situ by oxidation of its iron tricarbonyl complex) with p-benzoquinone yields A as the exclusive product. With tetracyanoethylene, however, B and C are formed in a 1 7 ratio. Discuss these results, and explain how they relate to the question of the square versus rectangular shape of cyclobutadiene. 

Arylation of enamines with p-benzoquinones takes a somewhat different course (70). The enamine (16) reacts exothermally with p-benzoquinone in benzene solution to give 2-(dimethylamino)-2,3-dihydro-3,3-dimethyl-5-benzofuranol (92). The reaction of enamines with quinone dibenzenesul-fonimide proceeds similarly (68). The product from the enamine (28) is the tetrahydrocarbazole derivative (93). 

Reactions of quinones with enamino ketones have not been reported, but ethyl (S-anilinocrotonate (94), an enamino ester, has been shown to condense (71) with p-benzoquinone to give l-phenyl-2-methyl-3-carbethoxy-5-hydroxyindole (95). 

The following unusual cyclization took place by the reaction of p-benzoquinone coordinated by palladium with two moles of butadiene at 60°C to give the tricyclic compound, 128 (117). 

Enthalpies, Activation Energies, and Rate Constants of Reactions of p-Benzoquinone with Phenols and Amines InH + Q > In + HQ in Hydrocarbon Solutions Calculated by IPM Method for Equations See Chapter 6 and for the Values of a, bre, and A, See Table 18.9... 

In 1981, a stereoselective palladium-catalyzed 1,4-diacetoxylation of 1,3-dienes with p-benzoquinone (BQ) as the oxidant was reported33. It was found that chloride ions can be used as a stereochemical switch. Thus, in the absence of chloride ions trans diacetoxylation takes place, whereas in the presence of a catalytic amount of chloride ion (as added LiCl) a cis diacetoxylation takes place (Scheme 4). In both cases the reaction is highly 1,4-regioselective. The explanation for... 

The use of a nitrogen nucleophile in the side chain (as an amide) also leads to an intramolecular 1,4-addition under the standard conditions for the palladium-catalyzed 1,4-oxidation reactions52. Nitrogen nucleophiles employed for this reaction comprise tosy-lamides, carboxamides, carbamates and ureas. The reactions are run in acetone-acetic acid with p-benzoquinone (BQ) as the oxidant. In most cases highly stereo- and regioselective reactions were obtained and some examples are given in Table 3. 

In general, 2,3-dialkyl-p-benzoquinones exhibit site selectivity in that they tend to give predominantly Diels-Alder adducts resulting from diene attack on the external rather than the internal double bond. This external site selectivity is, however, dramatically reversed when a (substituted) cyclobutane ring is fused to p-benzoquinone. Paddon-Row and coworkers103 studied the reactions of p-benzoquinones such as 129 with several... 

Reaction of tropolone with p-benzoquinone and spontaneous dehydrogenation yield 3-(p-benzoquinonyl)tropolone (106), which is hydrogenated and cyclized to give benzofurotropone 107 (62BCJ349, 62MI1). 

Problem 19.35 Write a structural formula for the product of the Diels-Alder reaction of p-benzoquinone with ... 

VO(oxine)2] (138) and [VO(oxine)2py]-C6H6 (140), prepared by a ligand displacement reaction (equation 61), had v(V==0) = 963 and 945 cm and pcS = 1.75 and 1.64 BM, respectively. When 8-quinolinol is replaced by 2-methyl-8-quinolinol in reaction (61), [VO(2-Me-oxine)2] is obtained, with v(V=0) = 970 cm-1. Complexes (138) and (140) react readily with 02 and a diamagnetic dinuclear pi-oxo Vv species [(oxine)2—OV—O—VO(oxine)2] is produced.826 Nitrobenzene and 2-nitrosobiphenyl also react in a similar manner in THF giving the same complex. With p-benzoquinone a dinuclear diamagnetic Vv complex [(oxine)2OVOC6H4OVO(oxine)2] is obtained. 

Benzo[6]furans and 2,3-dihydrobenzo[6]furans have been obtained by condensation of quinones with compounds having an active methylene group (B-74MI31201) and 2-aminobenzo[6 ]furan derivatives are obtained with malononitrile (68M2359). The reaction of p-benzoquinone with enamines also affords benzo[6]furans. 

Fig. 13. Reaction of 2,3-dimercaptopropanol with p-benzoquinone. Phosphate buffer pH 6.8, x 10 4M dimercaptopropanol, benzoquinone concentration (1) 0 (2) 0.59 (3) 1.15 (4) 1.74 (5) 2.3 X 10-4.M. Curves starting 0 V, S.C.E., 00 mV/absc h = 50 cm, full scale sensitivity 3.2 jjlA. Reaction between dimercaptopropanol and benzoquinone is fast, curves recorded immediately after mixing. Anodic wave of 2,3-dimercaptopropanol decreases and is replaced at very positive potentials by hydroquinone wave...

Velikyan I, Acharya S, Trifonova A, Foldesi A, Chattopadhyaya J (2001) The pffas of 2 -hydroxyl group in nudeosides and nucleotides. J Am Chem Soc 123 2893-2894 Veltwisch D, Asmus K-D (1982) On the reaction of methyl and phenyl radicals with p-benzoquinone in aqueous solution. J Chem Soc Perkin Trans 2 1147-1152 Vialas C, Pratviel G, Claparols C, Meunier B (1998) Efficient oxidation of 2 -deoxyguanosine by Mn-TMPyP/KHSOs to imidazolone dlz without formation of 8-oxo-dG. J Am Chem Soc 120 11548-11553... 

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