I3,=37Hz =3.7Hz Il3 =1.8 HZ z -2 3 i 5 6 80 70 60 50 -6 ippml Figure 1 . IH-NMR spectrum of 1,2-naphthalene oxide (in CC14; 60 MHz; tetramethylsilane as internal standard). No absorption beyond T = 6.2.1,2 Naphthalene oxide is obtained as a colorless crystalline compound that in the solid state rapidly rearrangessometimes with explosive violenceto a-naphthol. The presence of 1 ,Znaphthalene oxide follows unequivocally from the N M R spectrum reproduced in Figure 1. If the isomeric oxepin derivative ( 2 ) were present, then the signals corresponding to the protons H3 and H4 would appear at lower field strengths and, furthermore, the absorption due to H4 would be a singlet. The electronic spectrum of the oxide [maxima at 220 (E = 17600). 268 (8850). and 304 nm (1570) in dioxane] is remarkably similar to that of benzonorcaradiene 121. This finding rules out the possibility that 1,2-naphthalene oxide is in equilibrium with a significant concentration of the isomeric oxepin ( 2 ) . which is doubtless colored.Compound ( I ) is relatively stable in solution (ether). In the presence of catalytic amounts of a protic or a Lewis acid it spontaneously isomerizes to a-naphthol. Attempts to convert ( I ) into the known trans-l,2-dihydronaphthalene-l,2diol[71 have been unsuccessful. The fact that a number of authors have recently invoked 1,2-naphthalene oxide and other arene oxides as intermediates in enzymatic oxygenations of aromatic compounds 17981 seems a further justification for the publication of these results.
Synthesis of I,2-Naphthalene Oxide
a) 4-Bromo-I,2-epoxy-l.2,3,4-tetrahydronaphthalene (4)N-Bromosuccinimide (7.1 2 g, 40 mmole) and a,or'-azoisobutyrodinitrile (0.1 g) are added to a solution of 1,2-epoxy-1.2,3,4-tetrahydronaphthalene (3) (5.84 g. 40 mmole) in CC14 (75 ml). Once the reaction has'/ been started by quickly heating the mixture to boiling, no more heat has to be supplied. Succinimide and unreacted N-bromosuccinimide are filtered off and the filtrate is concentrated under vacuum until the bromide ( 4 ) begins to precipitate. On cooling to -lO°C, the main part of ( 4 ) crystallizes out in almost pure form; a further crop of ( 4 ) is obtained by working up the mother liquor. Recrystallization from ether/ethyl acetate (5:l) affords 2.1 g of (4) (23 % yield) having m.p. 94-95 OC (decomp.). b) l,2-Naphthalene Oxide ( I ) 1,5-Diazabicyclo[4.3.O]non-5-ene (400 mg, 3.2 mmole) is added dropwise,with stirring at 0 OC under an NZ atmosphere, to 4-bromo-1 ,bepoxy-l,2,3,4-tetrahydronaphthalene (4) (450 b.0mg. 2 mmole) in tetrahydrofuran (5 ml). The reaction mixture is stirred for 12 h at O°C and then allowed to stand for a further 12 h at this temperature. The tetrahydrofuran is evaporated off a t O°C under vacuum and the residue is treated first with 15 ml of pentane and then with 2 ml of water. The aqueous phase is extracted once again with 15 ml of pentane and the combined pentane solutions are washed three times with dilute KOH and dried over KzCO3. On cooling to -80°C, (1) crystallizes out as colorless needles...
