RATE CONSTANTS FOR 5-EXO AND 6-EXO SECONDARY ALKYL RADICAL CYCLIZATIONS ONTO N,N-DIPHENYLHYDRAZONES

Competitive ''radical clock''-type cyclizations of hydrazones and alkenes established that the rate constants for 5-exo cyclizations onto N,N-diphenylhydrazones are 1.1 x 10(8) s(-1) and 4.6 x 10(7) s(-1) at 80 degrees C to the cis- and trans-cyclopentylhydrazines, respectively (about 200 times faster than the corresponding cyclization rate for 5-exo alkenes). The 6-exo hydrazone rate constant is 9.4 x 10(5) s(-1) at 80 degrees C for both cis and trans isomers with activation barriers of 5.6 and 6.2 kcal/mol, respectively.