Table 1.

Rate constants and yields for the cycloadditions of DIBO (2) with various nitrile oxides

Entry	R	k (M-1 s-1)	Yield (%)a
1	C6H5b, c, d (5a)	3.38 ±0.03g	93
2	C6H5b, c, d (5a)	2.46 ± 0.03h	ND
3	4-MeO-C6H4b, e (5b)	2.15 ± 0.02g	89
4	4-O2N-C6H4b, f (5c)	8.47 ± 0.03g	93
5	4-F-C6H4b, c, d (5d)	3.99 ± 0.05g	90
6	4-Cl-C6H4b, c, d (5e)	3.42 ± 0.03g	90
7	4-Br-C6H4b, c, d (5f)	3.31 ± 0.06g	93

^aIsolated yields of combined isomers.

^bSecond order rate constants were determined from pseudo first order rate constants at various concentrations of in situ formed nitrile oxides at 25 ± 0.1°C.

^cPseudo first order kinetics were determined using UV-Vis spectroscopy by following the decay of the absorbance of compound 2 at 305 nm.

^d[2] = 6.0 × 10^-5 M; for details on the concentrations of nitrile oxides, see supporting information.

^e[2] = 3.0 × 10^-5 M; [5b] = 2.5-5.0 × 10^-4 M.

^fPseudo first order kinetics were determined by UV-Vis spectroscopy following the decay of the absorbance of 5c at 325 nm; [5c] = 6.0 × 10^-5 M, [2] = 7.0-17.5 × 10^-4 M.

^gReaction was performed in methanol.

^hReaction was performed in acetonitrile.