Concerted mechanism, technique demonstration

A review of direct observation of the transition state has traced the development of the femtosecond reaction dynamic technique, which has been used to demonstrate that the retro-Diels-Alder reaction can proceed by a stepwise mechanism as well as the usual concerted process.28 The oxide anion accelerated retro-Diels-Alder reaction has also been reviewed29 and the promise of this mild reaction for synthetic application has been emphasized. 

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