As a part of ongoing research to synthesize novel bicyclic thiones from bicyclic ketones, we have experimented with the action of different thionating reagents on the same bicyclic ketone; in addition to using the same thionating reagent on different bicyclic ketones. Different methods and/or conditions produced unexpected results with respect to reagent and ketone. For example, the treatment of (±) 1,7,7-trimethylbicyclo[2.2.1]heptan-2-one (camphor) with phosphorous pentasulfide (P2S5) in hexamethyl disiloxane (HMDSO) resulted in the formation of (±) 1,7,7-trimethylbicyclo[2.2.1]heptan-2-thione (~40%); resolved using gas chromatography - mass spectrometry. Replacing HMDSO with octamethyl trisiloxane (OMTS), however, increases the thione conversion to 99%. Similar results were obtained using 1,3,3-trimethylbicyclo[2.2.1]heptan-2-one. In sharp contrast, under the same conditions (P2S5/OMTS), (-)-1-isopropyl-4-methylbicyclo[3.1.0 ]hexan-3-one (α-thujone, 1) afforded no detectable thione and 90% p-Cymene (2) (Figure 1). The conversion of α-thujone to β-thujone under the aforementioned conditions was also noted. With P2S5, sodium bicarbonate (NaHCO3) and carbon disulfide (CS2), (±) 1,7,7-trimethylbicyclo[2.2.1]heptan-2-one (3) yields 41% of the corresponding thione (4) and 13% of 1,7,7-trimethylbicyclo-2,2,1-heptan-2,2-dithiol (5)(Figure 2). Possible mechanistic explanations are presented.

Unusual products from the thionation of bicyclic ketones

2019 Spring National Meeting

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