1-Methyl-1,4-cyclohexadiene as a Traceless Reducing Agent for the Synthesis of Catechols and Hydroquinones

Abstract

Pro-aromatic and volatile 1-methyl-1,4-cyclohexadiene (MeCHD) was used for the first time as a valid H-atom source in an innovative method to reduce ortho or para quinones to obtain the corresponding catechols and hydroquinones in good to excellent yields. Notably, the excess of MeCHD and the toluene formed as the oxidation product can be easily removed by evaporation. In some cases, trifluoroacetic acid as a catalyst was added to obtain the desired products. The reaction proceeds in air and under mild conditions, without metal catalysts and sulfur derivatives, resulting in an excellent and competitive method to reduce quinones. The mechanism is attributed to a radical reaction triggered by a hydrogen atom transfer from MeCHD to quinones, or, in the presence of trifluoroacetic acid, to a hydride transfer process.

Expanding the spectrum of polydopamine antioxidant activity by nitroxide conjugation

“…The presence of a quinone-rich outer shell also explains why PDAn is a good trap for reducing radicals such as HOO • and O2 •-(see Scheme 2). 3,11,40 In this case, the radicals reduce the ortho-quinone moieties to the corresponding semiquinones, which in turn possess radical trapping capabilities toward oxidizing ROO • radicals.…”

Hydrogen Atom Transfer from HOO. to ortho‐Quinones Explains the Antioxidant Activity of Polydopamine

“…Results, reported in Figure 1 B, indicated a smaller and a higher HOOC trapping ability than the corresponding quinones for 1H 2 and 2H 2 respectively. [26] The use of CHD as the only oxidizable substrate simplifies the analysis of autoxidation kinetics, propagated only by HOOC [X = H in Eqs. ( 8) and ( 10)], since reactions ( 5) and ( 6) become unimportant.…”

Reaction with ROO• and HOO• Radicals of Honokiol-Related Neolignan Antioxidants

“…The reduction of all quinones is attributed to the release of HOO• during the autoxidation of CHD which acts as the reducing agent. This uncommon reducing behavior might be counterintuitive for a reputedly oxidizing radical, but it is supported by previous solid evidence [ 44 , 45 , 46 ].…”