Gas‐Phase Kinetics of Pyrolysis of 3,3‐Dimethylcyclopropene and Its 1‐Trimethylsilyl Derivative The Effect of Silyl Substitution on Cyclopropene Isomerisation

Abstract

Abstract The gas‐phase pyrolysis of 3,3‐dimethylcyclopropene ( 1 ) in the temperature range of 185–225°C gives 3‐methyl‐1‐butyne ( 2 ) (91%) and isoprene ( 3 ) (9%). The gas‐phase pyrolysis of 3,3‐dimethyl‐1‐trimethylsilylcyclopropene ( 4 ) in the temperature range of 195–235°C gives 3‐methyl‐1‐trimethylsilyl‐1‐butyne ( 5 ) (99%) and trans ‐3‐methyl‐1‐trimethylsilyl‐1,3‐butadiene ( 6 ) (1%). Both rearrangements are homogeneous, first‐order, unimolecular reactions with the following pressure‐independent Arrhenius parameters. magnified image Rather surprisingly, the trimethylsilyl group deactivates cyclopropene with respect to its isomerisation. Possible mechanisms are discussed.