A novel titanium tetrachloride-induced rearrangement of an enantiopure 4-naphthyldioxolane. The possible role of titanium in the umpolung of tosyloxy and chlorine

The rearrangement of (2′S,4′R,5′S)-2-(2′,5′-dimethyl-1′,3′-dioxolan-4′-yl)-4,5,7-trimethoxynaphthalen-1-yl 4″-methylbenzenesulfonate with titanium(IV) chloride affords (1R,3S,4R)-10-chloro-6,7,9-trimethoxy-1,3-dimethyl-3,4-dihydro-4-hydroxynaphtho1,2-c]pyran in good yield. This transformation is characterized by two unusual aromatic substitution reactions in that, in one, tosyloxy is lost and, in the other, aromatic chlorination occurs with titanium(IV) chloride as the source of chlorine.