2-Methoxy-l,4-benzoquinone

Engler and colleagues256 demonstrated that the way in which catalyst 406 is prepared has a strong effect on the regioselectivity and enantioselectivity of quinone Diels-Alder reactions. The most effective catalyst was prepared from a 1 1 1 mixture of titanium tetrachloride, titanium tetraisopropoxide and chiral diol 416. The cycloadditions of 2-methoxy-l,4-benzoquinones such as 414 with simple dienes to give adducts like 415 proceeded with high yields and enantioselectivities of up to 80% ee using this catalytic system (equation 123). 

Hie GOG-Dimer formed from the lignin dimer compound (GOG) by laccase III was also degraded by laccase HI, resulting in the formation of compounds (I), (VI), and biphenyl dimer of 2-methoxy-l,4-benzoquinone (DC). This indicates that GOG-Dimer also suffers the cleavage of -0-4 ether linkage via the alkyl-phenyl cleavage. 

Wu et al. reported the total synthesis of clausenaquinone A (112) using a palladium(ll)-mediated oxidative cyclization of the 2-arylamino-5-methoxy-l,4-benzoquinone 874 (107). This total synthesis was undertaken to establish the structure of natural clausenaquinone A (112). The key intermediate, 2-(3-hydroxy-4-methylanilino)-5-methoxy-l,4-benzoquinone (874), required for this synthesis, was obtained by the reaction of 5-amino-o-cresol (873) with 2-methoxy-l,4-benzoquinone (872) which was readily obtained by oxidation of methoxyhydroquinone (871). The palladium(ll)-mediated oxidative cyclization is non-regioselective. Thus, the cyclization of the 2-arylamino-5-methoxy-l,4-benzoquinone 874 with palladium(Il)... 

Phenoxazin-3-ones and phenothiazin-3-ones can be prepared by condensation of 2-aminophenols or -thiols with quinones. Alizarin Green G (61), for example, is obtained from (59) and (60). Similarly, 2-aminothiophenols and 6-chloro-2-methoxy-l,4-benzoquinone (62) afford phenothiazin-3-ones (63). 

The results of irradiating the pora-quinoid structures (compounds 1-4) absorbed onto cellulose sheets are summarized in Figure 2. Examination of the photolysis data indicates that with the notable exception of 2-methoxy-l,4-benzoquinone the remainingpara-quinone model compounds did not cause any further darkening of the handsheets during irradiation. Indeed, several of the quinones exhibit a minor brightening response upon photolysis which could be attributed to a photo-bleaching effect, but the lack of a complete mass balance makes this conclusion tenuous. 

The reactions of ketene acetals with Schiff bases derived from (S)-valine esters 1.59 (R = /-Pr) under TiCl4 catalysis are highly selective, but the chiral auxiliary has not been removed [264], Engler and coworkers [1532] performed the asymmetric [2+2]-cycloaddition of 2-methoxy-l,4-benzoquinone with 1-arylpro-penes substituted by electron-donating groups. These reactions occur at -78°C when catalyzed by chiral titanium complexes derived from 2.50 (R = Me, Ar = R = Ph). Cycloadducts are obtained with a good selectivity (Figure 9.6). 

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