Optically active diols, starting materials

The optically active c/.v-epoxide 60, the key starting material for construction of the carbon framework of 46 and 47, was prepared as depicted in Scheme 13. The diol 54 was easily obtained from diethyl L-tartrate according to Saito s procedure. Activation of the primary hydroxyl group of 54 by tosylation was followed by base treatment, affording the epoxide 55 in 63% yield. Transformation of 55 into the vinyl derivative 56 was realized as follows. Addition of the acetylide, prepared from trimethylsilylacetylene and butyllithium ("BuLi), to 55 in... 

The Roche group extended this work and in 1981, at the 6th International Symposium on Carotenoids in Liverpool, reported the total synthesis of several of the ten optical isomers of e,8-carotene-3,3 -diol (tunaxanthin, 149) and of four diastereoisomers of p,e-carotene-3,3-diol, including the most common (3R,3 / ,6 / )-isomer, lutein (133). The starting material for these syntheses was 6-oxoisophorone, which the Roche scientists went on to use to synthesize a large number of dicyclic carotenoids in optically inactive and active form, as reported at the 7th International Symposium on Carotenoids in Munich in 1984. 

The starting material for the synthesis of the optically active vicinal diol (266) was (+)-(55,65)-5,6-dihydroxy-5,6-dihydro-P-ionone (260) (Eschenmoser et al., 1982). To synthesize the polyenoid side chain, (260) was first converted to the 5-trimethylsiloxy compound (261), which was then condensed with the C5 phosphonate (231) to give (262). 

For example, in the case of oxiranes and thiiranes one must prepare first the corresponding chiral 1,2 diols, and the overall yields from starting materials to final cyclic monomers are sometimes less than 5%. Price and Osgan [1] were the first to polymerize with different initiators the dextrorotatory propylene oxide. Several other optically active oxiranes and thiiranes were successfully prepared and polymerized [2, 3]. 

---