Synthesis and Structure of 1,8-Dimethoxy-10-methyl-9-methylene-9H-thioxanthenium Salt—Possibility of Hypervalent Bonding Through O─C─O (?)

Abstract

1,8-dimethoxy-10-methyl-9-methylene-9H-thioxanthenium salt (4) was prepared and the structure was determined by X-ray analysis to show the bond length between O─C is 2.80 A. This is too long to effect a hypervalent bonding. Bis[(1,8-dimethoxy) thioxanthylidene]allene (5) was prepared to be a symmetric compound in solution. Methylation of 5 with Meerwein reagent afforded S-monomethylated product (6) in solution and 6 gradually decomposed to C (or S)-monoprotonated allene (7), which was separately prepared as stable compound.

Keywords:

• 1,8-Dimethoxythioxanthylidene
• (bisthioxanthylidene)allene
• hypervalent bonding
• methylation
• protonation