Studies on Reactions of Thioketones with Trimethyl(trifluoromethyl)silane Catalyzed by Fluoride Ions

Abstract

Treatment of 2,2,4,4-tetramethylcyclobutane-1,3-dione (6) in THF with CF 3 SiMe 3 in the presence of tetrabutylammonium fluoride (TBAF) yielded the corresponding 3-(trifluoromethyl)-3-[(trimethylsilyl)oxy]-cyclobutanone 7 (Scheme 1) via nucleophilic addition of a CF À 3 anion at the CO group and subsequent silylation of the alcoholate. Under similar conditions, the −monothione× 1 reacted to give thietane derivative 8 (Scheme 2), whereas in the case of −dithione× 2 only the dispirodithietane 9, the dimer of 2, was formed (Scheme 3). A conceivable mechanism for the formation of 8 is the ring opening of the primarily formed CF 3 adduct A followed by ring closure via the S-atom (Scheme 2). In the case of thiobenzophenones 4, complex mixtures of products were obtained including diarylmethyl trifluoromethyl sulfide 10 and 1,1-diaryl-2,2-difluoroethene 11 (Scheme 4). Obviously, competing thiophilic and carbophilic addition of the CF À 3 anion took place. The reaction with 9H-fluorene-9-thione (5) yielded only 9,9'-bifluorenylidene (14; Scheme 6); this product was also formed when 5 was treated with TBAF alone. Treatment of 4a with TBAF in THF gave dibenzhydryl disulfide (15; Scheme 7), whereas, under similar conditions, 1 yielded the 3-oxopentanedithioate 17 (Scheme 9). The reaction of dithione 2 with TBAF led to the isomeric dithiolactone 16 (Scheme 8), and 3 was transformed into 1,2,4-trithiolane 18 (Scheme 10).

Four‐Membered Heterocycles: Structure and Reactivity

“…Isomerization of cyclobutane-1,3-dithiones into thietanones occurs in the presence of strong bases [319]. Utilization of tetrabutylammonium fluoride, allows a transformation under milder conditions (Scheme 3.178) [320]. The same product is obtained by reaction of the cyclobutane-1,3-dione with P 4 S 10 at reflux in pyridine [321].…”

Adamantanethione

“…Unexpectedly, 9 is also formed in good yield (69 %) on treatment of a solution of 1 in abs. THF with a catalytic amound of TBAF 32 as well as in the presence of silica gel in dichloromethane solution. 18 eq (6) 7…”

2,2,4,4-Tetramethylcyclobutane-1-one-3-thione

“…54 The reaction of 1 with (trifluoromethyl)trimethylsilane (Ruppert's reagent) in THF in the presence of fluoride yields the trifluoromethylated thietane 56 (eq 23). 55 A plausible mechanism of the transformation is a ring-opening/ring-closure process initiated by nucleophilic addition of trifluoromethanide to the carbonyl group of 1. Miscellaneous.…”