Secondary deuterium isotope effects on both rate and product determining steps in the thermolysis of 4-methylene-1-pyrazoline

Abstract

The secondary deuterium kinetic isotope effect in the thermolysis of 4-methylene-1-pyrazoline and four of its deuterated isomers has been studied. The value of δΔG≠/n is 142 cal mol−1 if it is a single C—N cleavage process or 71 cal mol−1 if it is a concerted rupture of two C—N bonds. The product distributions can only be rationalized in terms of a mechanism involving a rate determining C—N bond rupture to form a diazenyl diradical intermediate which then can close to methylenecyclopropanes by three possible modes. This requires a secondary isotope effect in the product determining step of 1.33 ± 0.05, for the rotation of CH2 (CD2) out of the plane of the allylic radical in the intermediate.

Sterically hindered nitrogen inversion in five-membered cyclic hydrazines

“…‡ Compounds of the type C (R = Me, Et) were described. 9 § Pyrazolidines D (R = H, PhCO), 11 E (X = CH 2 , R = CO 2 Et), 12 (X = = Me 2 C, R = CO 2 Et) 13,14 and F (R = H, R' = Me) 15 were described. (Pr i NH) 2 C H 4 J (H3)(H5) = -1.5 Hz).…”

Synthesis of Methylene- and Alkylidenecyclopropane Derivatives

“…Several alkyl-substituted MCPs and ACPs were synthesized by this method. − In one case the methylene pyrazoline 106 was obtained from a pyrazolidinone by Wittig olefination . In another single case the pyrazoline 107 was obtained by reaction of a TMM diradical with diazodicarboxylate followed by decarboxylation and oxidation.…”