The Reactivity of Selenophene Compared with Thiophene and Furan

The Reactivity of Selenophene Compared with Thiophene and Furan 

Isotope exchange is a technique which gives reliable comparative data on the electrophilic and protophilic reactivity of the five-membered heterocycles furan, thiophene, and selenophene, revealing how the activity of their hydrogen atoms varies with the position of the hydrogen in the ring and with the number and position of substituents. The results from kinetic data on isotopic exchange in deuterated selenophenes, thiophenes, and furans, may be summarized as follows. 

When treated with lithium f-butoxide in DMSO, selenophene79,84 exchanges a-deuterium atoms approximately 1.5 times faster than 

The protophilic exchange rate for a-deuterium atoms differs from that for ft atoms by a factor of 50,000 in selenophene, 250,000 in thiophene, and 500 in furan. 

The structures below summarize hydrogen activities of selenophene, thiophene, and furan in protophilic isotope exchange the rate constant of deuterium exchange at the a position of furan is arbitrarily given the value of unity. 

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