Olefin metathesis of conjugated enynes

Abstract

1. Olefin Metathesis of Conjugated Enynes We demonatrated that the olefin metathesis of conjugated enynes with alkenes by use of a pyridine substituted ruthenium carbene catalyst. Although the chemical yields obtained were moderate with the use of the present catalytic system, it is an important result considering the utility of conjugated enynes in materials science and synthesis of biolactive molecules. In cross- metathesis, we can observe that the generated enynes have enhanced (Z)-olefin selectivities and the extent of that selectivity reaches up to >25:1 with a certain type of enyne substrate. It should be noted that the (Z)-selectivity observed in this study is highly unusual considering the fact that, in general, (E)-alkenes are favorably formed from the cross-metathesis between alkenes. On the other hand, intramolecular version of conjugated enyne metathesis affords a novel molecular skeleton of cyclic conjugated trienes, which is a highly useful building block in organic synthesis and is extremely difficult to be accessed with previously reported procedures. In addition, the synthetic utility of the generated cyclic conjugated trienes has been investigated by a Diels-Alder reaction. All substrates which were treated with tetracyanoethylene dienophile produced the desired cyclo-adduct in quantitative yields at mild condition within 10 minutes. 2. Synthetic Study on (+)-Allosedamine A concise synthesis of an (+)-allosedamine has been achieved by the hydrolytic kinetic resolution and ruthenium catalyzed ring closing metathesis. In this study, hydrolytic kinetic resolution (HKR) was used to obtain a high diastereoselective epoxide as a key intermediate. HKR has advatageous relative to the other reported methodolgy not only because of the simple reaction condition but also the reproducibility of diastereoselectivity in product. In addition, we could easily obtain the chiral styrene oxide, starting material of our synthetic scheme, from the cheap racemic sty...