Reactions of thianthrene cation radical with acyclic α, ω-diols: Formation of monoadducts and bisadducts. Intramolecular cyclization of monoadducts to cyclic ethers

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.

Keywords:

• Thianthrene cation radical
• α
• ω-Diols
• Cyclic ethers

Acknowledgements

We thank the Welch Foundation for support (Grant D-0028) and Mr. David W. Purkiss (TTU) for the 500-MHz NMR spectroscopy.