The product 4,4-di-tert-butyl-3-methyl-4H-l,2-oxazete 2oxide (2) is the first derivative of the new system 4H-1.2-.
oxazete. It was isolated in quantitative yield when a solution of ( I ) in ethanol, after having been allowed to stand overnight, was evaporated down and the residue recrystallized from ethanol.
The structure of (2), which melts at 85 "C and sublimes with spontaneous cyclization at 50 OC/lO-3 torr, is proved by the following findings: C,H,N analysis; molecular weight (calc. 199; found 205, osmometrically); N M R spectrum (in CDC13, 8 scale), 2 singlets at 1.2 and 2.1 ppm with relative areas 6:l; IR spectrum (in Cc14). strong band a t 1698 cm-1 in the stretching vibration region of C = N bonds in rings; UV spectrum, sharp band (half width 27 nm) at 222 nm, E = 7 . 4 ~ lo3 (nitrones have similar UV spectra) 121. On catalytic hydrogenation (room temperature; atmospheric pressure, Raney Ni, dioxane) the oxazete (2) slowly absorbs 1 molecular equivalent of hydrogen. The hydrogenation product (3) (m.p.
sublimes at 6OoC/10-2 torr) is characterized by the following data: C,H,N analysis; N M R spectrum (in CDC13). four singlets at 1.1, 2.1, 5.0, 8.9 ppm with relative areas 18:3:1:1 (the signal at 8.9 ppm shows the characteristic broadening of oxime protons); I R spectrum in (CCl4), two bands at 3594 and 3459 cm-1 in the 0 -H stretching region. Like other a-hydroxy oximes [31, compound
(3) forms a Cu2+ complex. The hydrogenation occurs as for isoxazoline N-oxides 141. The kinetics of the isomerization (1) -f (2) was studied in several solvents by measuring the decrease in extinction of the UV band of (I) at 345 nm. In all cases, the reaction was clearly of the first order. The velocity increases with increasing polarity of the solvent; half-reaction times are 140 h in nhexane, 70 h in diethyl ether, 2 h in ethanol. Solid ( I ) isomerizes to (2) within several weeks. The unusua1 cyclization must be due to the strong steric hindrance by the four substituents around the C=C bond. In compound ( I ) this hindrance is avoided by rotation around the C=C bond; in (2) this angle of twist amounts formally to 90". A similar strong rotation is observed also in the anion radical of ( I ) [*I. Compound (2) is stable to heat up to at least 100 "C and can be considered as a new example of stabilization of small rings by tert-butyl groups (51.