Divergent routes to chiral cyclobutane synthons from (-)-alpha-pinene and their use in the stereoselective synthesis of dehydro amino acids

Several polyfunctionalized cyclobutane derivatives have been synthesized us ing commercial (-)cll-pinene and (-)-verbenone as chiral precursors. Thus, oxidative cleavage of these compounds by using ruthenium trichloride afford ed quantitatively (-)-cis-pinonic and (-)-cis-pinononic acids, respectively , without epimerization. These products were converted into several types o f aldehydes, which are the key intermediates in the synthesis of cyclobutan e dehydro amino acids via Wittig-Horner condensations with suitable phospho nates. These reactions are highly stereoselective, affording exclusively (Z ) isomers, stereochemistry being assessed by NMR experiments. The obtained dehydro amino acids are polyfunctionalized molecules useful for the synthes is of other a-amino acids, with additional chiral centers, whose configurat ion must be induced by the chirality of the terpene employed as a precursor .