SYNTHETIC EQUIVALENTS OF CYCLOHEXATRIENE IN [4-CYCLOADDITION REACTIONS - METHODS FOR PREPARING CYCLOADDUCTS TO BENZENE(2])

The methods available today to obtain the cycloadducts that would form in the reactions of dienophiles with benzene are reviewed. Amongst th ese methods, the one which engages 1,3-cyclohexadienes substituted at the 5 and 6 positions with removable functional groups will be discuss ed in more detail. Substituents must be chosen carefully so that they do not interfere with the reactivity of both dienophile and diene (if possible they should activate the cycloaddition) and so that they do n ot fall apart to form an aromatic molecule. Such 5 and 6 protected 1,3 -cyclohexadienes can be prepared using several different methods, one of which consists of a double cycloaddition of a dienophile on properl y substituted dienes. Because the overall result is. the preparation o f a cycloadduct performed on benzene, in the very same way as it react ed as a cyclohexatriene, these molecules can be considered as equivale nts of cyclohexatriene in [4+2]-cycloaddition reactions.