Ozonolyses of indene and of 1-alkyl- and 1,1-dialkyl-substituted indenes in protic solvents. Remarkable effects of the substituent steric bulk and the solvent nucleophilicity on the direction of cleavage of the primary ozonides and on the mode of capture of the carbonyl oxide intermediates by the solvents

Ozonolyses of indene (1a) and of 1-alkyl- and 1,1-dialkyl-substituted indenes 1b-h in protic solvents including methanol, 2-propanol, and trifluoroethanol revealed that (i) two types of the solvent-derived products, a hemiperacetal and/or an isochroman derivative, are produced depending on the nucleophilicity of the solvent and the steric bulk of the alkyl substituent(s), and (ii) the regiochemistry of the fragmentation of a primary ozonide is a marked function of the nature of the 1-alkyl-substituent. In the case of indene (1a) and 1-substituted indenes 1b-e, both possible modes of primary ozonide cleavage operate competitively yielding two carbonyl oxide intermediates in roughly equal amounts, whereas in the case of 1,1-dialkyl-substituted indenes 1f-h the contribution of the less-hindered carbonyl oxide predominates. © 1995 American Chemical Society.