Formation and thermal cleavage reactions of the cycloadduct of 9,10-dimethylanthracene and nitrosyl cyanide

Abstract

Nitrosyl cyanide and 9,10-dimethylanthracene (DMA)(2) reacted at –25 °C to form the crystalline cycloadduct, 9,10-dihydro-9,10-(N-cyanoepoxyimino)-9,10-dimethylanthracene (1). The adduct (1) decomposed in the presence of the conjugated diene thebaine (3), to form DMA (2) and the adduct (4) of nitrosyl cyanide and thebaine. First-order kinetics, k= 6.9 × 10^–5s^–1, were observed for the release of DMA in benzene at 40 °C, consistent with slow dissociation of the adduct (1) followed by rapid capture of nitrosyl cyanide by thebaine. A similar first-order rate, k= 6.8 × 10^–5s^–1, was observed for the reaction of the adduct (1) and triphenylphosphine (2 mol equiv.) under the same conditions, the products being DMA, triphenylphosphine oxide, and triphenylphosphine N-cyanoimide (5). The reactions of nitrosyl cyanide, generated thermally from the adduct (1), were studied with a range of dienes. The conjugated dienes, N-cyanomethyl-N-northebaine (3; NCH₂CN replacing NMe), trans,trans-1,4-diphenylbuta-1,3-diene (6; R = H), and ergosteryl acetate (11) all gave the expected cycloadducts (3,6-dihydro-2H-1,2-oxazines). Norbornadiene gave the tetracyclic adduct (10) arising from 1,4-conjugate addition of nitrosyl cyanide. The reactions of the adduct (1) with tetraphenylcyclopentadienone (14), 1,3-diphenylisobenzofuran (18), 2-methyl-1,3-diphenylisoindole (23), diazofluorene (24), and diphenyldiazomethane all took a more complex course leading in each case to the formation of an N-cyano-ketimine (alkylidene-cyanamide)