Favorskii‐rearrangement in the presence of 3,4‐dimethoxyfuran: preparation of 3,4‐dimethoxy 11endo****‐oxo‐tricyclo [4.3.1.1^2,5^]undec‐3‐en‐10‐one and any derivatives
On treatment with sodiumhydride of 2‐chloro‐cyclohexanone in the presence of 3,4‐dimethoxyfuran, a possible intermediate of the Favorskii‐rearrangement has been trapped as 3,4‐dimethoxy‐11__endo__‐oxa‐tricyclo [4.3.1.1^2,5^]undec‐3‐en‐10‐one (3). This new compound contains a highly nucleophilic double bond. It can be cleaved in high yield by ozonolysis to 2__exo__, 4__exo__‐bis (methoxycarbonyl)‐3‐oxabicyclo [3.3.1]nonan‐9‐one (4). Addition of chlorine to 3 occurs in stereoselective exo‐cis‐manner to the crystalline 3__exo__, 4__exo__‐dichloro‐3__endo__,4__endo__‐dimethoxy 11__endo__‐oxa‐tricyclo [4.3.1.1^2,5^]undecan‐10‐one (5). Silver ion assisted hydrolysis of 5, followed by thermal treatment of the intermediate hydrates, leads to the red 11__endo__‐oxa‐tricyclo [4.3.1.1^2,5^]undecan‐3,4, 10‐trione (6), and methanolysis to 3,3,4,4‐tetramethoxy‐11__endo__‐oxa‐tricyclo [4.3.1.1^2,5^]undecan‐10‐one (8). By photolytic decarbonylation, 8 is converted into 3,3,4,4‐tetramethoxy‐10‐oxa‐tricyclo‐[4.3.1^2,5^.0]decan (9).