P-quinone monoimide

Engler and coworkers [76] developed a new domino process which consists of a [5+3] cycloaddition of a p-quinone monoimide with a styrene derivative followed by a [3+2] or [3+3] cycloaddition. The reaction allows the formation of two additional rings and up to eight stereogenic centers, with high selectivity. The best results, with 58% yield of4-230, were obtained in the transformation of 4-227 and 4-228 in the presence of BF3 Et20 at -20 °C (Scheme 4.49). In addition, the diastereomer 4-231 was obtained in 16 % yield. It can be assumed that the cation 4-229 functions as an intermediate. The process also functions with quinones, though much less efficiently. 

In the absence of a Lewis acid promoter, the 2 + 3-reaction between p-quinone monoimide and azadienes, e.g. a,-unsaturated hydrazones yielded 2,3-dihydroben-zofurans in moderate to excellent yields when the dienophile was maintained at low concentration.43... 

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]. 

Oxidative demethylation A new approach to indoloquinones such as 5 involves Michael addition of ethyl acetoacetate to the quinone monoimide 1 to give 2, which is dehydrated to the indole 3 in 73% overall yield. The latent quinone ring is then modified to give the p-methoxyaniline 4. The final step involves the oxidative demethylation reaction of Rapoport (4, 431-432) to give an intermediate quinone imine, which is hydrolyzed to 5. 

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