PHOTOINDUCED WOLFF-REARRANGEMENT OF 2-DIAZO-1-NAPHTHOQUINONES - EVIDENCE FOR THE PARTICIPATION OF A CARBENE INTERMEDIATE

Photolysis of sodium 2-diazo-1-oxo-1,2-dihydronaphthalene-5-sulfonate and 4-tert-butylphenylphenyl 2-diazo-1-oxo-1,2-dihydronaphthalene-5-su lfonate in aliphatic alcohols results in the formation of a high yield of the corresponding sodium 3-(alkoxycarbonyl)-1H-indene-5-sulfonate and 4-tert-butylphenyl 3-(alkoxycarbonyl)-1H-indene-5-sulfonate, respe ctively. 1-Hydroxy-2-alkoxynaphthalene-5-sulfonates are formed as side products in these photoreactions. The observed maximum molar yield of the latter products was 8.8%. Photolysis of a solution of sodium 2-di azo-1-oxo-1,2-dihydronaphthalene-5-sulfonate in water yields, apart fr om the main photoproduct, sodium 3-carboxy-1H-indene-5-sulfonate, appr oximately 15% of the sodium 1,2-dihydroxynaphthalene-5-sulfonate. Both the nature of the side products of the photoreaction, as well as thei r yield as a function of the concentration of alcohol and water in var ious solvent mixtures, are a strong indication for the presence of a c arbene intermediate in the reaction mechanism. Picosecond transient ab sorption measurements show that the internal conversion and vibrationa l relaxation to the ground state in the two diazo compounds mentioned above, takes place within 8 ps after excitation. The photofragmentatio n and formation of indenylidene-ketene is also completed within this s ame time period. In the case of 2-diazonaphthalen-1(2H)-one, the vibra tional relaxation and photofragmentation take place within 8 ps, but i n this particular case, a precursor of the ketene could be observed. T his precursor has a decay rate constant of 5 x 10(10) s(-1) and is pro posed to be the carbene.