Thianthrene cation radical tetrafluoroborate (Th.+BF 4-) added to the terminal alkynes 1-pentyne, 1-hexyne, 1-heptyne, 1-octyne, 1-nonyne, and 1-decyne to form trans-1,2-bis(5- thianthreniumyl)-alkene tetrafluoroborates (1-6). Similarly, addition of phenoxathiin cation radical tetrafluoroborate (PO.+BF 4-) to the same alkynes gave 1,2-bis(10-phenoxathiiniumyl) alkene tetrafluoroborates (7-12). The trans configuration of two of the adducts (1 and 4) was shown with X-ray crystallography. When solutions of 1-6 in chloroform were stirred with activated alumina, cis elimination of a proton and thianthrene (Th) occurred with the formation of 1-(5-thianthreniumyl)alkyne tetrafluoroborates (1a-6a). Similar treatment of 8-12 caused elimination of a proton and phenoxathiin (PO) with formation of 1-(10-phenoxathiiniumyl)alkene tetrafluoroborates (8a-12a). Stirring of 1a-6a with alumina for short periods of time caused their conversion into 5-[(α-keto)alkyl]thianthrenium ylides (1b-6b) and α-ketols, RC(O)CH2OH (1c-6c).
ASJC Scopus subject areas
- Organic Chemistry