Ozonolysis of 1-methylindenes. Solvent, temperature, and substituent electronic effects on the ozonide exo/endo ratio

The ozonolyses of 1-methyl-3-aryl-, 1,2-dimethyl-3-aryl-, and 1-methyl-2,3-diarylmdenes (1a-e, 4a-e, 7a-e, 7a',b',d') in various solvents at several temperatures have been undertaken. The data revealed the following. (a) The ozonolysis of indenes 1c, 4c, and 7c in aprotic solvents yielded in each case a mixture of exo/endo ozonide isomers, the solvent-independent exo/endo ratio being 7:3, 3:2, and 3:7, respectively. In marked contrast, protic solvents exerted a significant influence on the ozonide stereochemistries. (b) The ozonolysis of indene 7c in methanol at -70°C afforded a novel methanol-participated product 14 as the major product, whereas the reaction at 20 °C lead to the production of a 72% yield of the expected ozonide isomers 8c/9c. A similar trend was observed for 4c. From 1c, however, a more conventional methanol-participated product 10 was obtained along with ozonide isomers 2c/3c. (c) The ozonide exo/endo ratios increased with the decrease of the reaction temperature. The exception was the ozonolysis of 4 in MeOH, in which the reverse trend was observed. (d) The substituent electronic effect can exert a significant influence on the ozonide composition. © 1985 American Chemical Society.