The novel preparation of butenolides and 3,4-disubstituted furans: Approaches towards halenaquinone.

Part 1: Palladium catalyzed cross-coupling reaction. Many aryl bromides will undergo a palladium catalyzed cross-coupling reaction with 3- ((t-butyldimethylsilyl) oxymethyl) -4-(tri-n-butylstannyl)furan to form a new class of 3,4-disubstituted furans in excellent yields. The reaction is fast and easy to perform. It also represents an expansion of the scope of the cross-coupling reaction as it provides examples of rare aryl tin-aryl bromide couplings. Part 2: Lead tetraacetate oxidations of 2-(trialkylsilyl)furans. The treatment of 2-(t-butyldimethylsilyl)furan with lead tetraacetate in warm (70$\sp\circ$C) acetic acid provides 2-acetoxy-3-(t-butyldimethylsilyl)-$\Delta\sp3$-butenolide and 4-acetoxy-4-(t-butyldimethylsilyl)-$\Delta\sp2$-butenolide in a 2:1 ratio and 90% yield. The formation of the major product may involve a rare acid catalyzed 1,2-silyl migration. The reaction proceeds slower in refluxing chloroform providing the products in a 1:1 ratio and slightly lower yields. The altered ratio may be due to a much lower acid concentration. The reaction does not tolerate bulky or aryl groups on the silicon atom. Part 3: Synthetic approaches towards halenaquinone. Synthesis of the natural product Halenaquinone was attempted. Difficulties were encountered in the 6-membered ring closing step to form a tetrahydroisobenzofuran. The C-4 iodine on the furan ring resisted reaction to carbanion and carbon radical generating techniques.Dept. of Chemistry and Biochemistry. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis1990 .B668. Source: Masters Abstracts International, Volume: 30-03, page: 0739. Thesis (M.Sc.)--University of Windsor (Canada), 1990