Abstract
Potential energy hypersurfaces of the nitrogen elimination and the Wolff rearrangement were investigated for both cyclic and open-chain 2-diazoketones by means of semi-empirical MINDO/3 molecular orbital calculations with configuration interaction. In the cases of 2-diazobenzen-l-one and cis-2-diazoethan-1-one, the nitrogen elimination takes place simultaneously with the Wolff rearrangement in a concerted fashion and neither ketocarbene nor oxirene is produced. The potential energy changes were shown in Fig. 2 and Fig. 9, respectively, and the molecular structure changes following the reactions were in Figs. 4 and 10. In contrast, 2-diazoethan-1-one in trans-conformation produces oxirene through nitrogen elimination in a concerted fashion. The oxirene isomerizes to ketene via the Wolff rearrangement, passing over a second saddle point of low energy (Fig, 5). The reaction sequence is shown in Fig. 8. No ketocarbene intermediate is produced in any case. A new mechanism of the Wolff rearrangement was proposed as in Fig. 14(b). This mechanism explains experiments well while the old mechanism (Fig. 14(a)) is inconsistent with experiments occasionally. It was concluded that the photochemical reaction of the diazonaphthoquinone-novolac resist mainly taking place in microlithography process is one-step ketene formation as shown in Fig. 1(c).
