Azulenequinones, cycloaddition

High-pressure cycloaddition reactions of 3-bromo-1,5-azulenequinone and 3-bromo-1,7-azulenequinone with dienophiles [68]... 

Takeshita and colleagues299 studied the reactions of 3-bromo-l,5-azulenequinone (478) and 3-bromo-l,7-azulenequinone (484) with benzo[c]furan (479) and 1,3-diphenylbenzo [c]furan (485) by analogy with the reactions previously described by Scott and Adams300. The reaction of 478 with 479 afforded a mixture of four cycloadducts (equation 142), three stereoisomeric [2 + 4]/[6 + 4] tandem adducts (480-482) and one [2 + 4]/[2 + 4]/[6 + 4] triple adduct (483). No mono adduct was isolated, indicative of a fast follow-up cycloaddition. The [6 + 4] cycloadditions all proceeded in an exo fashion, whereas the [4 + 2] cycloaddition proceeded in an endo fashion for 480 and 483, and in an exo fashion for 481 and 482. The reaction of 478 with 485 afforded a mixture of [4 + 2] adducts and [4 + 2]/[8 + 4] tandem adducts. 

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