Abstract
Reactions of thianthrene cation radical tetrafluoroborate () with α, ω-diols, HO(CH2)
n
OH (4b–g, n=5, 6, 8–10, 12), at the molar ratio Th•+:4 2/1 in MeCN containing 2,6-di-tert-butyl-4-methylpyridine (DTBMP) led to formation of bisadducts, α, ω-di(5-thianthreniumoxy)alkane ditetrafluoroborates (7b–g). Reactions with 4b,c gave also the cyclic ethers 6b,c by intramolecular cyclization. Preparation of the bisadduct (7a) from 1,4-butanediol (4a) was achieved only in the absence of DTBMP, in low yield. The major product was tetrahydrofuran (THF, 6a). Reactions of
with 4b–g in the molar ratio 1/6, carried out in MeCN without DTBMP, led to the formation of monoadducts, α-hydroxy-ω-(5-thianthreniumoxy)alkane tetrafluoroborates (5b–g). Reactions with 4b,c led again also to cyclic ethers 6b,c. Cyclization of adducts to ethers (6b,c) was confirmed with the isolated monoadducts (5b,c). Attempts to prepare a monoadduct (5a) from 4a were unsuccessful; only THF (6a) was obtained. 5b–g and 7a–g were characterized with 1H and 13C NMR spectroscopy. Reactions of 7b,c with basic alumina resulted in formation of 4b,c rather than in elimination of thianthrene oxide and formation of linear dienes.
Acknowledgements
We thank the Welch Foundation for support (Grant D-0028) and Mr. David W. Purkiss (TTU) for the 500-MHz NMR spectroscopy.