
%0 Journal Article
%A Clark-Lewis, JW 
%A Jemison, RW 
%T Flavan derivatives. XXIII. Preparation and synthetic applications of Flav-3-enes
%J Australian Journal of Chemistry
%D 1968/09/01
%V 21
%N 9
%P 2247-2254
%K 
%R https://doi.org/10.1071/CH9682247
%U https://www.publish.csiro.au/paper/CH9682247 
%X 2'-Hydroxychalcones and &#945;-alkoxy-2'-hydroxychalcones are converted by sodium borohydride in isopropanol into flav-3-enes and 3-alkoxyflav-3-enes in the convenient new synthesis which makes these flavenes readily available. Catalytic reduction of the flavenes gives the corresponding flavans or 3-alkoxyflavans in high yield, and the latter are obtained mainly in the 2,s-cis-form. The flavenes immediately give flavs lium cations in the cold when treated with acids in air, and oxidation of 5,7,3',4'-tetramethoxyflav-3-ene with benzoquinone in an acidic medium gave the flavylium salt, isolated as the ferrichloride. Reduction of 5,7,3',4'-tetramethoxy-flavylium chloride with lithium aluminium hydride gave 5,7,3',4'-tetramethoxy-flav-2-ene identical with the flavene obtained from (-)-epicatechin tetramethyl ether, and confirms an earlier investigation by Gramshaw, Johnson, and King. In its N.M.R. spectrum the heterocyclic-ring protons of this flav-2-ene give an ABX multiplet which is easily distinguished from the ABX multiplet at much lower field characteristic of flav-3-enes. 
