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■ Synthesis of (S)- and (R)-Sporochnol by Using the Allylic Substitution of the Secondary Allylic Picolinate

Yuichi Kobayashi,* Yusuke Sugihara, Toshifumi Tojo, and Takuri Ozaki

*Department of Biomolecular Engineering, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Box B52, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226-8501, Japan

Abstract

The allylic substitution of secondary allylic picolinates and copper reagents for the construction of a quaternary carbon was applied to synthesis of sporochnol. The enantiomerically enriched allylic picolinate (R)-5 was synthesized through the asymmetric hydrogen transfer of acetylene ketone 11 and the Pd-catalyzed methylation of the iodoallylic alcohol 16a. The key allylic substitution of the allylic picolinate (R)-5 with 4-MeOC6H4MgBr/Cu(acac)2 (2:1) proceeded with 95% chirality transfer with 98% regioselectivity to afford anti SN2' product 6 in 89% yield, which was converted to the methyl ether of unnatural (R)-sporochnol. Similarly, the methyl ether of (S)-sporochnol (the natural form) was synthesized.