Asymmetric Synthesis Of The Side Chains Of Brassinolide And Studies On The Transition Metal Catalyzed Reaction And Applying In The Synthses

This thesis mainly aims at the studies on novel construction of the side chains ofbrassinolide and related compounds, and the asymmetric total synthesis of(4R,5S)-O-Acetyl-Osmundalactone, and studies on the platinum catalyzed reaction.It mainly consists of the following three parts:PartⅠ: Novel construction of the brassinolide and related compounds' sidechains.1. We report here a new method for constructing the side chains of brassinolide fromsteroidal-aldehyde, which is stereoselective and produces high yields. The key stepsof this routes included a highly stereoselective asymmetry aldol reaction induced bythe chiral aldehyde, the epimerization of a position of carbonyl and asymmetryhydrogenation induced by the chiral intermediate.2. Novel phenomenon that the silyl groups migrated fromα-oxygen toβ-oxygen inlithium and sodium aldol reaction ofαposition ofα-silyloxy ketone was observed forthe first time in this paper.PartⅡ: The asymmetric total synthesis of (4R,5S)-O-Acetyl-Osmundalactone.Efficient asymmetric total synthesis of (4R,5S)-O-Acetyl-Osmundalactone has beencarried out in several steps from L-ethyl lactate. The key steps included Sharplessasymmetric epoxidation and RCM reaction.PartⅢ: The platinum catalyzed reaction.A platinum catalyzed cycloisomerization of 1,6-enyne coupling with therearrangement chemistry of propargylic ester has been developed. Most probably,under platinum catalysis, propargylic ester undergoes the 1,3-acyloxy migration to afford metal allene intermediate, which is followed by the Diels-Alder type reaction.1,3-Acyloxy migration is the key step during the transformation.