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.
The absolute configurations at 8 and 9-carbons of Adda, an amino acid component of a hepatotoxin, cyanoviridin RR
作者:TSUKUDA, T.、KAKISAWA, H.、PAINULY, P.、SHIMIZU, Y.
DOI:——
日期:——
Convergent Enantioselective Synthesis of Vinigrol, an Architecturally Novel Diterpenoid with Potent Platelet Aggregation Inhibitory and Antihypertensive Properties. 1. Application of Anionic Sigmatropy to Construction of the Octalin Substructure
作者:Leo A. Paquette、Ronan Guevel、Shuichi Sakamoto、In Ho Kim、Jason Crawford
DOI:10.1021/jo0301301
日期:2003.8.1
The coupling of building blocks 15 and 36e in the presence of MgBr(2).OEt(2) at 0 degrees C proceeds with an exo stereoselectivity (3.2:1) considerably more advantageous for the acquisition of carbinol 37e than in the absence of the additive (exo/endo = 1:5.7). The pivotal transformation that sets all of the relevant stereocenters of the cis-octalin 55 is the oxyanionic-accelerated [3,3]-sigmatropic