102948-87-8Relevant academic research and scientific papers
Electro-organic reactions. Part 54: Quinodimethane chemistry; Part 2 - Electrogeneration and reactivity of o-quinodimethanes
Utley, James H.P.,Ramesh, Shalini,Salvatella, Xavier,Szunerits, Sabine,Motevalli, Majid,Nielsen, Merete F.
, p. 153 - 163 (2007/10/03)
The electrochemical generation and characterisation of a variety of o-quinodimethanes (o-QDMs) are described together with the outcome of preparative experiments in which they are key intermediates. The quinodimethanes are conveniently formed, in DMF, by both direct and redox-catalysed electroreduction of 1,2-bis(halomethyl)arenes. Their predominant reaction is polymerisation to poly(o-xylylene) (o-PX) polymers. In the presence of dienophiles the electrogenerated o-QDMs may undergo efficient cycloaddition reaction and distinctions between the possible mechanisms have been attempted on the basis of voltammetric, preparative and stereochemical experiments. Contrary to the precedent of the corresponding methyl ester, diphenyl maleate radical-anion isomerises only slowly to the fumarate radical-anion, yet co-electrolysis of 2,3-bis(bromomethyl)-1,4-dimethoxybenzene and diphenyl maleate or diphenyl fumarate gives exclusively the corresponding trans-adduct. Co-electrolysis of dimethyl maleate with either 1,2-bis(bromomethyl)benzene (more easily reduced) or 2,3-bis(bromomethyl)-1,4-dimethoxybenzene (less easily reduced) gave only o-PX polymer. The results are rationalised in terms of a double nucleophilic substitution mechanism where electron transfer between dienophile radical-anion and dihalide is relatively slow. Where electron transfer from maleate or fumarate radical-anions is likely to be fast o-quinodimethanes are formed by redox-catalysis and they polymerise rather than undergo Diels-Alder reaction. Dimerisation of the dienophile radical-anions, with k2 = 104 to 105 M-1 s-1, does not apparently compete with nucleophilic substitution or, where relevant, electron transfer.
Reaction of phenyl-substituted o-quinodimethanes with nitric oxide. Are benzocyclobutenes suitable precursors for nitric oxide cheletropic traps?
Paul, Thomas,Hassan, Mohammed A.,Korth, Hans-Gert,Sustmann, Reiner,Avila, David V.
, p. 6835 - 6848 (2007/10/03)
In order to elucidate the potential of substituted o-quinodimethanes as reagents for the trapping of nitric oxide (NO) in biological systems, the reaction of alkoxyl- and alkyl-substituted 7,8-diphenyl- and 7,7,8-triphenyl-o-quinodimethanes with nitric oxide in solution was investigated by ESR spectroscopic and UV/vis stopped-flow techniques. Photolytic decarbonylation of 1,3-diphenyl- and 1,1,3-triphenylindan-2-ones gave the corresponding phenyl-substituted benzocyclobutenes as the major products and low photostationary concentrations of o-quinodimethanes. During 266-nm laser flash photolysis (LFP) of 1,3-dimethoxy-1,3-diphenylindan-2-one and 1-methoxy-1,3,3-triphenylindan-2-one in acetonitrile, species absorbing in the 400-600 nm range were produced, which were attributed to configurational isomers of the corresponding 7,7,8,8-substituted o-quinodimethanes. The isomeric o-quinodimethanes decayed at significantly different rates, indicating a strong influence of the relative orientation of the terminal substituents on their stability. Reaction of the raw photolysates of the 2-indanones with NO produced strong ESR spectra of the corresponding cyclic nitroxide radicals, isoindolin-2-oxyls. The nitroxide radicals were generated in a two-phase process, the first, rapid phase being attributed to the reaction of NO with the photolytically formed o-quinodimethanes and the second, slow phase reflecting the reaction with small amounts of o-quinodimethanes, generated by thermal ring opening of the phenyl-substituted benzocyclobutenes and probably a direct reaction of NO with the benzocyclobutenes. The kinetics of both steps, as evaluated by stopped-flow UV/vis and ESR spectroscopy, revealed a strong dependence of the rate constants of the o-quinodimethane ± NO reaction on the substitution pattern of the o-quinodimethanes, with rate constants spanning a range of 10-4000 M-1 s-1. The rate constants ((0.4-7.5) x 10-4 s-1) for the reaction of NO with the 7,7,8,8-tetrasubstituted benzocyclobutenes are much less influenced by the substitution pattern. The utility of phenyl-substituted benzocyclobutenes as 'reservoirs' for o-quinodimethane-type nitric oxide traps is discussed.
