Cycloaddition Reactions of More Than Six Electrons Systems -, -, -, -, -, and -Cycloadditions

Some cycloaddition reactions of more than six ji electron systems have been reported. Thermal suprafacial [its+ s] [ s + s] [its + 7Cs] y lo ditions are forbidden according to Woodward-Hofifmann rules. These cycloadditions are photochemically allowed processes. Thermal antarafacial [itj + 7c a] addition is possible, but is rare. The following examples are illustrative for [4+4]- and [6+61-cycloadditions  

Thermal [6h-4]- and [12-I-2]-cycloadditions are allowed processes. Among them, [6-i-4]-additions are common. These additions are favored than D-A cycloaddition reaction because of the largest coeflSdents of HOMO and LUMO. The following 

N-Ethoxycarbonylazepine 139 dimerizes to 140 on heating, where one molecule acts as a 6ji system and other as a 4ji electron component. 

3-Pentadiene reacts with tropone to give [6+4]-cycloadduct 141. 

Conjugated Sit electron systems undergo thermal [8+2]-cycloaddition reactions with 2jt electron system. The following examples are illustrative  

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