IN PURSUIT OF CYCLOPROPANETHIONE - CYCLOPROPANETHIONE S-OXIDE AND S,S-DIOXIDE

The geometries of cyclopropanethione (1a), methylenethiirane (2a), cyclopropanethione S-oxide (1b), methylenethiirane S-oxide (2b), cyclopropanethione S,S-dioxide (1c), methylenethiirane SS-dioxide (2c), thioformaldehyde SS-dioxide (sulfene), and the tetramethyl derivatives of 1b and 2b, tetramethylcyclopropanethione S-oxide (1d) and 3,3-dimethyl-2-isopropylidenethiirane S-oxide (2d), respectively, were optimized at the SCF level by using ab initio molecular orbital theory with a polarized double zeta basis set. The difference in energy for each pair of isomers is as follows: 2a more stable than 1a by 6.4 kcal/mol; 1b more stable than 2b by 8.2 kcal/mol; 2c more stable than 1c by 0.2 kcal/mol; and Id more stable than 2d by 0.3 kcal/mol. Fluorodesilylation of 1-(trimethylsilyl)cyclopropanesulfonyl chloride (3) in the presence of 1-(N,N-diethylamino)-1-propyne affords 4-(N,N-diethylamino)-3-methyl-2-thiaspiro[3.2]hex-3-ene 2,2-dioxide (19) in 56% yield by way of 1c. Treatment of cyclopropanesulfinyl chloride (7) with triethylamine gives triethylamine hydrochloride in 90% yield along with S-1-chlorocyclopropyl cyclopropanethiosulfonate (18), S-cyclopropyl cyclopropanethiosulfonate (9), and cyclopropanesulfonyl chloride (8). The formation of these latter four products is consistent with the intermediacy of 1b. Attempts to fluorodesilylate 1-(trimethylsilyl)cyclopropyl aryl disulfides generating cyclopropanethione 1a itself led instead to products derived from rearrangement of aryldithio alpha-cyclopropyl carbanions. A cyclopropanethione, dispiro[2.0.2.1]heptane-7-thione (20), which is calculated to be stable relative to its methylenethiirane tautomer, is proposed.