2-Diazo-1,3-dimesityl-2H-indene and 1,3-dimesitylisoindenylidene

Abstract

Reduction of 1,3-dihydroxy-1,3-dimesitylindan-2-one oxime 5 with HI–HOAc gives the primary enamine, 2-amino-1,3-dimesitylindene 7. This resists hydrolysis to 1,3-dimesitylindan-2-one 6 even with boiling concentrated HCl–dioxane (1 : 1); steric protection of C-3 by the mesityl group and an overwhelming preference for the enamine tautomer may account for the unusual stability of 7. With NaNO₂–HOAc 7 gives 2-diazo-1,3-dimesityl-2H-indene 2, the only known 2-diazoindene. The ¹³C and ¹⁵N NMR shifts of C-2 and the terminal nitrogen in 2 suggest somewhat greater diazonium indenylide character than for 1-diazoindene. Though isolable, 2 decomposes slowly at 20 °C or upon exposure to visible light to give the hydrocarbons 14, 15 and 16, which probably arise via 1,3-dimesitylisoindenylidene 3 and the o-quinodimethanes 18 and 19. The decomposition of 2 in the presence of oxygen, 4-phenyltriazoline-3,5-dione, and N-phenylmaleimide are described.