[3383-21-9]  · C14H20O2  · 3,5-Di-t-butyl-1,2-benzoquinone  · (MW 220.31)

(reacts with primary amines to give different products depending on the alkyl substituent: benzoxazoles from primary amines and a-amino acids; ketones from s-alkyl primary amines; dioxazepines from cyclopropylamines; aromatic aldehydes from vic-aminobenzyl alcohols; skatole from tryptophan)

Alternate Name: DTBBQ.

Physical Data: mp 114-115 °C.

Solubility: sol most organic solvents; insol water.

Form Supplied in: dark red needles; commercially available.

Analysis of Reagent Purity: by TLC (silica gel plate Bakerflex-IBF, hexane/methylene chloride (1:1), Rf 0.53);5 UV-vis lmax 402 (ε = 821).3

Preparative Methods: by PbO2 oxidation of 3,5-di-t-butylcatechol;7 by chemical and electrochemical oxidation of 3,5-di-t-butyl-2-hydroxyaniline.3

Purification: recrystallization from toluene or by vacuum sublimation.

Handling, Storage, and Precautions: avoid exposure to light; toxicity unknown.

General Characteristics.

As a result of the steric hindrance caused by two t-butyl groups, the reactions are centered at the less hindered carbonyl, producing an unstable quinoneimine which is prone to a spontaneous aromatization. All reactions occur under mild conditions. In several reactions DTBBQ mimics pyridoxal.8

Reactions with Amines.

Primary alkyl primary amines, e.g. benzylamine1 and ethanolamine,2 react with DTBBQ to give benzoxazole derivatives via a quinoneimine and a Schiff base that undergoes cyclization and dehydrogenation with DTBBQ present in excess (eq 1).

s-Alkyl primary amines undergo oxidative deamination (Corey's reaction) to give ketones produced in 84-97% yield. A small quantity of a phenoxazinone derivative is responsible for the pink color of the reaction mixture (eqs 2 and 3).1,3

The tertiary cyclopropyl primary amine 1-phenylcyclopropylamine reacts via a ring-opening step to form a substituted dibenzoxazepine and an azospirodecatrienone (eq 4). Also the products obtained with cyclopropylamine show evidence of ring cleavage.4

Vicinal aminobenzyl alcohols with 2 equiv of DTBBQ undergo C-C bond cleavage to form the respective aromatic aldehydes and benzoxazoles in high yields (eq 5). With an equimolar ratio of the reactants, benzaldehyde condenses with a portion of the amino alcohol to give the Schiff base (1).2,6

a-Amino acids form 2-substituted benzoxazoles via a decarboxylation step.5 Tryptophan is an exception, undergoing retroaldol cleavage and formation of skatole (eqs 6 and 7).6

1. Corey, E. J.; Achiwa K. JACS 1969, 91, 1429.
2. Mermersky, Y.; Horak V. Presented at the Joint South-Eastern and Mid-Atlantic ACS Regional Meeting, Washington, DC, December 1992.
3. Klein, R. F. X.; Bargas, L. M.; Horak, V. JOC 1988, 53, 5994.
4. Sayre, L. M.; Singh, M. P.; Kokil, P. B.; Wang, F. JOC 1991, 56, 1353.
5. Zwan, M. C. V.; Hartner, F. W.; Reamer, R. A.; Tull, R. JOC 1978, 43, 509.
6. Mermersky, Y. Thesis research, Georgetown University, Washington, DC; 1994.
7. Flaig, W.; Ploetz, T.; Biergans, H. LA 1955, 597, 196.
8. Martel, A. E. ACR 1989, 22, 115.

Vaclav Horak & Youco Mermersky

Georgetown University, Washington, DC, USA

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