The intramolecular diels-alder reaction as a route to synthetic lignan lactones

Immunosuppressive flavones and lignans from Bupleurum scorzonerifolium

“…The spectrum (228, 258, and 318 nm) indicated the presence of an arylnaphthalene lignan (Klemm et al, 1966). The IR {1759 cm À1 (C=O)} and the 13 C NMR { 171.38 s (C=O)}spectrum indicated the presence of a g-butyrolactone (Harrowven, 1993;Iwasaki et al, 1995).…”

“…Moreover, there were also NOE interactions between H-2 0 and H-6/2-CH 2 ( 5.02, 5.10) and 8-OMe ( 3.36), respectively. Thus, its structure was determined as 4-benzo[1,3]-dioxol-5-yl-5,6,7-trimethoxy-3H-naphtho[2,3-c]furan-1-one (3), which was previously obtained as a synthetic compound (Klemm et al, 1966), but is now described for the first time from a natural source and named chaihunaphthone (3). Analyses of HMBC, HMQC and COSY-45 data, furnished the complete 1 H and 13 C NMR assignment (Tables 1-3) for 1-3, 9-10, and 12.…”

Spectroscopic and computational evidence for the concerted mechanism of the Wagner‐Jauregg reaction

“…[16] The reaction was further improved by the discovery of Bruckner and Kovacs [17,18] that polymer formation could be significantly decreased by adding sub-stoichiometric amounts of various radical scavengers, including N,N-dimethylaniline (DMA). More recently, the intramolecular variant of the Wagner-Jauregg reaction has been applied to the synthesis of lignans [19] and other functionalized naphthalenes. [5,20] However, a lack of fundamental understanding about the Wagner-Jauregg reaction, including the reaction mechanism, has prevented its widespread application and most recent applications of the Wagner-Jauregg reaction can be found in the area of polymer research.…”

Synthesis of naturally occurring cinnamyl cinnamates

“…(E)-Cinnamyl (Z)-cinnamates have been used as intermediates for the synthesis of lignans. 10 A few methods are reported for the synthesis of (E)cinnamyl-(E)-cinnamates. These methods 10,11 involve reaction of cinnamoyl chloride with cinnamyl alcohol in the presence of base, or in situ reduction of carboxylic acids followed by esterification, using trimethylamine-borane 11a or involve palladium catalysed hydrocarboxylation 11b of allenes.…”

“…The method involving reduction of the triple bond of cinnamyl phenyl propiolate using Lindlar catalyst is reported for the synthesis of (E)-cinnamyl-(Z)-cinnamates. 10 Although these methods are reported for the synthesis of cinnamyl cinnamates, apart from 1f none of the naturally occurring compounds (1a-d, 2a and 2b) have been synthesised in sizable amounts. Their physical and spectral properties are also not reported in the literature.…”