Total synthesis of optically active integerrimine, a twelve-membered dilactonic pyrrolizidine alkaloid of retronecine type. I. Enantioselective synthesis of the protected (+)-integerrinecic acid
For the total synthesis of optically active integerrimine, the twelve-membered dilactonic pyrrolizidinealkaloid, the necic acid component (+)-integerrinecic acid has been enantioselectively synthesized in the protected form.
A total synthesis of the natural enantiomer of integerrimine (1), a twelve-membered dilactonic pyrrolizidinealkaloid of retronecine type has been achieved through the enantioselective synthesis and regioselective coupling of (+)-retronecine (4) and (+)-integerrinecic acid (methylthio)methyl ether (6).
Stereoselective synthesis of the pyrrolizidine alkaloids (-)-integerrimine and (+)-usaramine
作者:James D. White、John C. Amedio、Samuel Gut、Susumu Ohira、Lalith R. Jayasinghe
DOI:10.1021/jo00034a017
日期:1992.4
Two routes to the pyrrolizidine alkaloid (-)-integerrimine (1) are described. The first, starting from methyl (R)-(-)-3-hydroxy-2-methylpropionate, proceeded in 19 steps to integerrinecic acid lactone (5) which was transformed to the necic acid derivative 30. The latter was coupled to protected retronecine 31, and the synthesis of 1 was completed by lactonization employing Vedejs' protocol. A second, shorter synthesis of (-)-1 was accomplished via 5, starting from (R)-(+)-beta-citronellol (36). This pathway invoked Katsuki-Sharpless epoxidation of 42 for stereoselective construction of the tertiary alcohol of integerrinecic acid. A parallel sequence proceeding via the stereoisomeric epoxide 44 led to the necic acid segment 75 of the alkaloid (+)-usaramine (2). This acid was coupled to the retronecine borane 82 and then lactonized to 2.
WHITE, JAMES D.;JAYASINGHE, LALITH R., TETRAHEDRON LETT., 29,(1988) N 18, 2139-2142