Development of Novel Carbon-Carbon Bond Fragmentation Reaction by Means of Samarium Diiodide and Its Application to the Synthesis of Physiologically Active Compounds

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Development of the chemistry of samarium (II) iodide has been of continuing interest in organic synthesis because of its quite unique and useful properties, such as poweful reducing ability in addition to the chemoselectivity. Although the variety of useful transformation using samarium diiodide are investigated to date, little attention has focused on the fragmentatin reaction. We have there fore attempted to develop an efficient method for the reductive carbon-carbon bond cleavage reaction by utilization of samarium diiodide and found that the reaction of gamma-halo carbonyl compounds with samarium diiodide afforded the regioselective fragmentation reaction products in high yields. When this reaction was applied to the gamma-helo ester, derived from monoterpene carvone, the useful chiral building block could be prepared.Using the chiral building block as a starting material, the synthesis of (-)-oudemansin A, an antitumour compound, was achieved stereoselectively. Moreover this synthetic strategy was applied to the efficinet synthesis of gamma-lactonic compounds, such as cis-whisky lactone and eldanolide. The biologically interesting piperidine alkaloids, (-)-anhydronupharamine, (-)-nupharamine, (-)-nuphenine and (+)-3-epinupharamine, and pyrrolizidine alkaloid, (-)-heliotidane, were also synthesized in optically pure forms. Finally stereoselective synthetic procedures for the necic acid components of macropyrrolizidine alkaloids, crobarbatic acid andintegerrinecic acid lactone were established by utilization of this fragmentation reaction as a key step.These results clearly indicated that the newly developed samarium diiodide promoted fragmentation reaction of gamma-halo esters is a useful reaction in the synthesis of various types of physiologically active compounds.