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2005
Alkaloids
U 0600
25- 199
Total Synthesis of the Tricyclic Marine Alkaloids (-)-Lepadiformine, (+)-Cylindricine C, and (-)-Fasicularin via a Common Intermediate Formed by Formic
Acid-Induced Intramolecular Conjugate Azaspirocyclization. — An efficient total
synthesis of the tricyclic marine alkaloids (-)-lepadiformine (X), (+)-cylindricine C
(XI), and (-)-fasicularin (XII) is presented, involving the preparation of a common azaspiro[4.5]decane intermediate (IX) by formic acid-induced intramolecular conjugate
azaspirocyclization of an acyclic ketoamide (VIII). The influence of substrate structure
on the cyclization outcome is studied. Thus, cyclization to give an azaspiro[4.4]nonane
(V) proceeds non-stereoselectively, while the corresponding azaspiro[4.5]decanes (III)
are formed with good stereoselectivity at the ring system. The formation of azaspiro[5.5]undecane from substrate (VI) is not achieved. — (ABE, H.; AOYAGI, S.;
KIBAYASHI*, C.; J. Am. Chem. Soc. 127 (2005) 5, 1473-1480; Sch. Pharm., Univ.
Pharm. Life Sci., Hachioji, Tokyo 192, Japan; Eng.) — Mischke
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