The chemistry of cycloheptatriene part XII : the thermal behaviour of substituted cycloheptatrienes : preliminary communication

cf. CA 63, 457a. The effect of substituents on 1-5 intramol. shifts of H in cycloheptatriene (I) was investigated at 100-140 Deg (CA 59, 14771b). Conversion of 7-substituted I to the 3-substituted isomer was accelerated by all of the substituents studied, including NMe2, OMe, SMe, Me, Ph, and CN, the rates varying between 700 for the NMe2 deriv. and 9 for the Me deriv. relative to the half-rate for unsubstituted I. Rates for conversion of 3-to 1-, 1- to 3-, 1- to 2-, and 2- to 1-substituted I were also measured. The 7-Me2N compd. was converted by 2 rapid and virtually irreversible steps to the 1-substituted compd., which was the only detectable isomer in the equil. mixt. At equil. the amts. of isomers decreased in the order 1-, 3-, 2-, 7- for electron-donating substituents, the differences being more pronounced as the electron-donating tendency became stronger. In this sequence the substituent is in formal conjugation with 3, 2, 1, and 0 double bonds, resp., of the trienic system. For Ph and CN substituents the 1-isomer was again the most prevalent, but the 3- and 2-isomers were present in equal amts. at equil. 7-Di-methylaminocycloheptatriene not only underwent a 1-5 H shift at 70-110 Deg but also yielded 5-7% benzene, the amt. of which increased slightly with increasing temp. Neither reaction was affected by the type of solvent used. [on SciFinder (R)]