Multienzymatic organo catalysis : metal free preparation of fragrances by means of a laccase oxo-ammomium ene-reductase alcohol dehydrogenase catalytic system

The oxidative rearrangement of tertiary allylic alcohols is an extremely valuable transformation of organic chemistry, which has been exploited for the preparation of several alfa,beta-unsaturated carbonyl compounds, among which the fragrances Jasmone and Geranial occupy a special place. However, most of the chemical oxidative rearrangements relay on reagents based on toxic Chromium salts, and are used in a stoichiometric amount. Recently, eco compatible regents have been developed, however the catalytic procedures are not economically sustainable. Here we report on a new catalytic system for the oxidation of tertiary allylic alcohols, comprised by a Laccase enzyme coupled with an organic oxa-ammonium salt. This new catalytic procedure has been applied to a large range of substrates to give the corresponding alfa,beta-unsaturated carbonyl compounds, often in a quantitative yield, among which the fragrances Jasmone and Citral. Few years ago in another work it was coupled the ene-reductase (ERED) catalysed reduction of prochiral alfa,beta-unsaturated carbonyl compounds with an alcohol dehydrogenases (ADH) catalysed reduction of the carbonyl group to give the corresponding alcohols in high yields and with a good stereoselectivity. We have now expanded this multi-enzymatic process by coupling the Laccase mediated oxidation of a tertiary allylic alcohols with an ERED catalysed reduction of the newly generated conjugated C=C double bond, followed by the carbonyl reduction with an ADH to give more complex products.