Lignans and Their Degraded Derivatives from Sarcostemma acidum
摘要:
Four lignans, sacidumlignans A-D (1-4), and two degraded lignan derivatives, sacidumols A (5) and B (6), along with four known compounds, (+)-pinoresinol, 9alpha-hydroxypinoresinol, perforatic acid, and peucenine-7-O-methyl ether, were isolated from the ethanolic extract of the whole plant of Sarcostemma acidum. The structures and relative configuration of these new compounds were elucidated on the basis of spectroscopic and chemical data, especially 2D NMR techniques. Sacidumlignan D (4) was assigned as a rearranged tetrahydrofuran lignan with an unprecedented skeleton. Sacidumlignan A (1) showed moderate antimicrobial activities against two Gram-positive bacteria in vitro.
Triflimide-catalyzed allylsilane annulations of benzylic alcohols for the divergent synthesis of indanes and tetralins
作者:Jordan C. T. Reddel、Weiwei Wang、Kalli Koukounas、Regan J. Thomson
DOI:10.1039/c6sc04762a
日期:——
development of a triflimide-catalyzed annulation of benzylic alcohols with allylsilanes for the synthesis of indane or tetralin structures is reported. In this fragment coupling reaction, complexity is built rapidly from readily available starting materials to yield diverse sets of products with up to three contiguous stereocenters. Indanes or tetralins can be generated from common precursors depending
The first total synthesis of naturally occurring sacidumlignans A (1), B (2), and D (4) was executed and the absolute configuration of 2 and 4 was determined. A diastereoselective alpha- methylation of a lactone was used as the key step for the control of the chiral centers of the central lignan core. An acid mediated dehydrative cyclization of an aldehyde to construct the dihydronaphthalene unit of 2 and the aromatization of the intermediate dihydronaphthalene derivative to synthesize 1 are the key reactions employed in this regard.