Stereoselective hydrogenation of methylcyclohex-2-ene-1,4-diols used in the synthesis of ampelomins and deoxy-carbasugars

Stereoselective hydrogenation of methylcyclohex-2-ene-1,4-diols used as important intermediates for the preparation of ampelomins and deoxy-carbasugars was studied. These olefins were obtained in few steps from a chiral cis-diol resulting from microbial oxidation of toluene. Although the stereoselective hydrogenation of this type of substrates is difficult, high yields were obtained for heterogeneous hydrogenation using Adam's catalyst, where steric hindrance controlled the stereochemical outcome of the process. On the other hand, for homogeneous hydrogenation of similar olefins using Crabtree's catalyst, coordination with the allylic alcohols allowed for a controlled hydrogen addition from the more hindered face. In this manner two protocols for the hydrogenation of these types of substrates resulting in complementary stereoselectivities are described.