Chemistry around pinene and pinane: a facile synthesis of cyclobutanes and oxatricyclo-derivative of pinane from cis- and trans-pinanols.

Alpha-pinene and beta-pinene are abundantly represented in nature; they are obtained from renewable sources and are irreplaceable synthons for commercial-scale production of other terpenes. In a well-known process practiced by Millennium Specialty Chemicals (MSC), hydrogenation of pinenes gives cis- and trans-pinanes, which are oxidized to hydroperoxides, whose reduction gives cis- and trans-pinanols, respectively. Pyrolysis of the pinanols gives linalool. Industrial availability of the pinanols makes them attractive objects for further synthetic research. We found that, in a very simple process of 'chlorooxidation', cis- and trans-pinanols react with hypochloric acid producing a novel chloroketone 1-[3-(2-chloroethyl)-2,2-dimethylcyclobutyl]ethanone and a tricyclic ether 6,9-dimethyl-7-oxatricyclo[4.3.0.0(3,9)]nonane, respectively. Both compounds offer new broad synthetic opportunities, providing access to numerous dimethylcyclobutane derivatives and to C(9)-functionalized pinenes and pinanes. The chlorooxidation reaction was also extended to other terpene alcohols such as dihydroplinol, tetrahydromyrcenol, and tetrahydrolinalool. This review, based on a presentation at the RSC/SCI conference Flavours & Fragrances 2007 in London, September 24-26, 2007, will touch on environmental issues related to pinenes, give a brief overview of the existing pinene-based technologies, and discuss the new experimental results.