Abstract
The titanium tetrachloride-induced isomerisation of rel-(2R,4R,5S )- and re/-(2S,4R,5fl)-2,5-dimethyl-4-{8- bromo-4,5,7-trimethoxy-2-naphthyl) dioxolanes 16, having the C-4 oxygen protected by a methyl instead of the previously employed isopropyl group, afforded the desired linear re/-(1fl, 3fl,4fl)-6-bromo-3,4- dihydro-4-hydroxy-7,9,10-tnmethoxy -1 ,3-dimethyM H-naphtho[2,3-c] pyran 20, identified as its acetate 21, as well as the corresponding angular analogue, re/-( 1 fl,3R,4fl)-3,4-dihydro-4-hydroxy-6,7,9-trimethoxy- 1 ,3-dimethylnaphtho [1 ,2-c] pyran 22 also identified as its acetate 23…