Benzoquinone monoketals

Fig. 3.24 Oxidation of anisoles to p-benzoquinones monoketals catalysed by [Ru(CF3COO)2(Hp)(tmtacn)]+ [261]...

Benzofurancs, 346 Benzo[[Pg.292]

Likewise, the oxidative dearomatization ofpara-methoxy substituted N-protected anilines 288 using (diace-toxyiodo)benzene in the presence of methanol gives p-quinone monoimide ketals 289 (Scheme 3.120) [358]. If the oxidation of aniline derivatives is performed in the presence of water, the final isolated products are the respective / -benzoquinones or p-benzoquinone monoketals resulting from the hydrolysis of initially formed monoimide ketals 289 [358,359]. 

Various approaches to the assembly of the 1,3-dienes that engage in the Diels-Alder cycloaddition reactions leading to substrates for DPM and ODPM processes have been reported. Thus, for example. Yen and Liao demonstrated, during the course of a total synthesis of the Lycopodium alkaloid magellanine, that oxidation of acetovanillone (109) rScheme 9.151 with diacetoxyiodobenzene (DAIB) in the presence of methanol afforded the o-benzoquinone monoketal 110. The latter conpound engaged in an in situ Diels-Alder reaction with added cyclopentadiene (111) and the resulting adduct 112 proved to be an excellent substrate for the ODPM rearrangement reaction. Thus, photolysis of 112 as a solution in acetone afforded the pivotal tetracyclic diketone 113 in 92% yield. 

Treatment of a 2,5-disubstituted 1,4-dimethoxybenzene 877 with CAN provided a 97% yield of p-benzoquinone 878 °. The fully substituted 1,4-dimethoxybenzene derivative 879 was treated with CAN to afford in 64% yield the quinone monoketal 880. This was submitted to catalytic hydrogenation to give the precursor of a-tocopherol 881 (Scheme 178). A variety of substituted 1,4-dimethoxybenzenes were also oxidized with CAN to give high yields of p-benzoquinones. 

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