Syntheses and thermal reactions of cyclic sulphenium ylides: 2-alkyl (or aryl)-1-benzoyl-1H-2-thianaphthalen-2-ium-1-ides and 2-alkyl (or aryl)-1-benzoyl-3,4-dihydro-1H-2-thianaphthalen-2-ium-1-ides

Abstract

Pummerer cyclisation of phenacyl phenethyl sulphoxide (5) was carried out using trifluoroacetic anhydride to give 1-benzoyl-3,4-dihydro-1H-2-thianaphthalene (6) in good yield. Alkylation (or arylation) of 1-benzoyl-1H-2-thianaphthalene (1) and the 3,4-dihydro derivative (6) afforded 2-thianaphthalenium salts (2) and 3,4-dihydro-2-thianaphthalenium salts (7), respectively. 2-Alkyl(or aryl)-1-benzoyl-1H-2-thianaphthalen-2-ium-1-ides (3) and 3,4-dihydro-1H-2-thianaphthalen-2-ium-1-ides (8) were synthesised by deprotonation of the corresponding sulphonium salts (2) and (7) respectively with triethylamine in high yields. The 2-thianaphthalen-2-ium-1-ides (3) underwent a thermal 1,2-rearrangement in refluxing benzene or toluene to give the 1H-2-thianaphthalenes (9), while the 3,4-dihydro-2-thianaphthalen-2-ium-1-ides (8) underwent a novel 1,4-rearrangement to afford the enol ethers (10). The 1,4-rearrangement proceeded by two different routes: intermolecularly for S-methyl-3,4-dihydro-2-thianaphthaleniumide (8a), and intramolecularly for the S-phenyl derivative (8e).