RING EXPANSION REACTION OF 4-SUBSTITUTED SULFONYLOXY)METHYL-3-METHOXYCARBONYL-2-ISOXAZOLINE 2-OXIDE METHANESULFONATES BY USE OF TITANIUM TETRABROMIDE

trans-4-Substituted ulfonyloxy)methyl]-3-methoxycarbonyl-2-isoxazoline 2-oxide (3a-d) were prepared through mesylation of the corresponding 5-hydroxymethyl derivatives (2a-d), which were prepared from trans-4-s ubstituted 3,5-bis(methoxycarbonyl)-2-isoxazoline 2-oxides (1a-d). Com pounds (3a-d) were then allowed to react with titanium tetrabromide to afford ring expansion products, cis-4-substituted roxy-3-methoxycarbo nyl-5,6-dihydro-4H-1,2-oxazines (4a-d).