J. zyxwvutsrqponmlk prakt. Chem. 338 (1996) 598-603 Journal fur praktische Chemie Chemiker-Zeitung zy 0 Johann Ambrosius zy Barth 1996 Originalbeitrage Full Papers On the Reaction of Nitrilium Salts with Tropones R. Abu-El-Halawa Nablus (Palestine), Al-Najah University, Department of Chemistry, and Al-Mafraq (Jordan), A1 El-Bayt University, W. Wirschun, A. H. Moustafa, and J. C. Jochims Konstanz, Fakultat fur Chemie der Universitat Received December 5th, 1995 respectively March 18th, 1996 Abstract. Tropone 2a and tropolone methyl ether 2b react with nitrilium salts (la-j) to give the bicyclic oxazolium salts 3,s. Cleavage of the N-C3a bond of 3 , s followed by y Chap- man rearrangement afford the stable N-acyliminium salts 4, 8. A crystal structure analysis for 3a is reported. AM1 calculations are in accord with the proposed mechanisms for the formation of 3,s and 4,s. Recently, Luk'yanov et al. zyxwvuts [ 1-41 and we [5-101 report- ed reactions of nitrilium salts 1 with carbonyl compounds (Scheme 1). Thus, with tertiary carboxamides N-acyla- midinium salts were obtained [5, 61. Mixtures of up to four different N-acylamidinium salts are formed by re- actions of nitrilium salts with secondary amides [7, 81. Aromatic aldehydes afford high yields of N-acylimini- urn salts [2, 91, while a$-unsaturated carbonyl com- pounds give either 4H- or 6H-1,3-oxadiaziniumsalts, or N-acyl- 1 -azonia-1,3-butadiene salts [4, lo]. A review of the reactions of nitrilium salts with carbonyl com- pounds has been published by Luk' yanov [ 11,cp. Scheme 1. zyxwvutsr R' R2 zyxwvutsrqponmlkjih d zyxwvuts d Here we report that, differently from reactions with other a$-unsaturated carbonyl compounds, nitrilium salts 1 react with tropones 2 to the bicyclic salts 3. Thus, the yellow crystalline product3a (85%) was formed on stir- ring a mixture of tropone 2a and the N-methylacetonitrilium salt la at low temperatures (-70 to 23 "C) in dichlorometh- ane. Compounds 3b-g were prepared correspondingly. The constitution of 3a was,proved by an X-ray struc- tural analysis, see Fig. 1, Table 1. Note the planar five- membered ring and the twisted double bonds of the seven-membered ring. In the lH NMR spectra (CD,CN) of compounds 3 the broad signal around 4.8 ppm is assigned to H3a. I R5CttcR4CRQ D + 1 Scheme 1 Reported Reactions of Nitrilium Salts with Carbonyl Compounds (counterions omitted)