3,3',5,5'-tetra-tert-butyldiphenoquinone, DPQ
The organic oxidant 3,3',5,5'-tetra-tert-butyldiphenoquinone (DPQ) is commercially available and can also be readily prepared by oxidation of the inexpensive o,o'-di-tert-butylphenol. DPQ is a two electron acceptor that forms o,o'-di-tert-p-bisphenol as product, which can easily be separated. Reoxidation using oxygen in the presence of base is possible in near quantitative yields, which means, that O2 can formally be considered as the terminal oxidant in these reactions. (M. S. Kharasch, B. S. Joshi, J. Org. Chem. 1957, 22, 1439. DOI)
Compared with benzoquinone, one of the advantages is the non-nucleophilic character of the reaction product. Thus, DPQ can be used in reactions with electrophiles without any interference.
Recent Literature
Cooperative carbene catalysis allows selective oxidative acylations of
alcohols with aldehydes even in the presence of amino groups by using a readily
available cheap organic oxidant. Quantum chemical calculations support the
suggested mechanism.
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A N-heterocyclic carbene catalyzes the oxidative esterification of various
aldehydes in the presence of 3,3',5'5-tetra-tert-butyldiphenoquinone to
yield hexafluoroisopropylesters, which are useful active esters for in situ
amide bond formation. This transition metal-free organocatalytic system also
enabled a mild oxidative azidation of aldehydes.
S. De Sarkar, A. Studer, Org. Lett., 2010,
12, 1992-1995.
A N-heterocyclic carbene catalyzes the oxidative esterification of various
aldehydes in the presence of 3,3',5'5-tetra-tert-butyldiphenoquinone to
yield hexafluoroisopropylesters, which are useful active esters for in situ
amide bond formation. This transition metal-free organocatalytic system also
enabled a mild oxidative azidation of aldehydes.
S. De Sarkar, A. Studer, Org. Lett., 2010,
12, 1992-1995.
The direct oxidative N-acylation reaction of primary amides with aryl/α,β-unsaturated
aldehydes was achieved in the presence of an azolium salt and an inorganic base
using 3,3′,5,5′-tetra-tert-butyldiphenoquinone as the oxidant. The
reaction provides an efficient approach for the synthesis of N-sulfonylcarboxamides,
N-sulfinylcarboxamides, and dicarboxyimides in good yield.
C. Zheng, Y. Liu, C. Ma, J. Org. Chem.,
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A broad range of functionalized Grignard compounds were coupled by using
diphenoquinone as an electron acceptor. The oxidative dimerization of
alkenylmagnesium reagents proceeds with complete retention of the
stereochemistry.
A. Krasovskiy, A. Tishkov, V. del Amo, H. Mayr, P. Knochel, Angew. Chem. Int. Ed., 2006,
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A N-heterocyclic carbene-catalyzed reaction of enals with α-diketones enables an
asymmetric construction of cyclopentenones in a highly diastereo- and
enantioselective manner. The protocol tolerates substrates with both aromatic
and aliphatic groups.
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An N-heterocyclic carbene-catalyzed oxidative LUMO activation of the β-cabons of
saturated carboxylic esters enables an efficient asymmetric access to lactams
and lactones. The method introduces functional groups at the typically inert
β-sp3 carbons of saturated esters. The use of HOBt as an additive
improves both yields and enantioselectivities of the reactions.
B. Liu, W. Wang, R. Huang, J. Yan, J. Wu, W. Xue, S. Yang, Z. Jin, Y. R. Chi, Org. Lett.,
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A N-heterocyclic carbene (NHC)-catalyzed intramolecular cyclization of
aldimines generated from 2-amino phenols and aromatic aldehydes provides
2-arylbenzoxazoles in good yields under mild conditions. The reaction tolerates
a broad range of functional groups.
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N-heterocyclic carbene/copper-cocatalyzed [4 + 3] annulations of
salicylaldehydes with aziridines provide the corresponding 1,4-benzoxazepinones
in good yields with exclusive regioselectivity.
Y.-F. Han, Z.-H. Gao, C.-L. Zhang, S. Ye,
Org. Lett., 2020, 22, 8396-8400.