Rearrangement of Terpene Epoxides

The isomerization of many terpene oxides (see Section 5.4) has been investigated using a wide range of solid acids (and bases). Arata and Tanabe are responsible for much of this work which includes d-limonene oxide [16], 2- and 3-carene oxide [17], and carvomenthene oxide [18]. 

More recently the isomerization of caryophyllene oxide has been investigated by Arata et al. [19] They reacted caryophyllene oxide (11) with a wide variety of solid acids (and some solid bases) and obtained varying ratios of up to five main products. The ratio of products formed was found to depend on the catalyst used. Catalysts such as FeS04 and Zr(S04)2 gave larger quantities of ketone product whereas allylic alcohols were preferentially formed over catalysts such as Ti02 Zr02 and AhO,. 

Another group has also reported a potential zeolite (H-US-Y)-catalyzed production process for preparation of campholenic aldehyde from a-pinene oxide which is described as competitive with the traditional zinc bromide process [21]. Other groups have also looked at this transformation [22]. 

Heterogeneous solid-acid catalysis has the potential to make a major contribution towards improving the environmental acceptability of terpene rearrangement and isomerization processes. There are potential heterogeneously catalyzed replacement processes for the production of campholenic aldehyde, an important intermediate for many fragrance compounds. With continuing advances in the field of solid-acid catalysis it is likely that other industrially useful heterogeneous catalysts will be discovered. 

See Chemistry of Fragrant Substances, Paul J. Teisseire, VCH Publishers, 1994. W. F. Fh)l-derich, D. Heinz, Catalysis, 1999, 14, 148. 

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