[17008-22-9] · C3H3NS2 · Methyl Cyanodithioformate · (MW 117.21)
(electron-deficient thiocarbonyl compound; readily undergoes Diels-Alder and ene reactions with dienes and alkenes, respectively; reacts readily with amines)
Physical Data: deep purple; bp 50-60 °C/1 mmHg.
Preparative Method: addition of Sodium Cyanide to Carbon Disulfide in DMF affords sodium cyanodithioformate, which is converted to the unsolvated tetraethylammonium cyanodithioformate by treatment with tetraethylammonium bromide in ethanol. Reaction of the tetraethylammonium salt with excess Iodomethane in acetonitrile for 1 min provides methyl cyanodithioformate in 65% yield.1
Handling, Storage, and Precautions: dimerizes on standing and in the presence of nucleophiles. It should be prepared immediately before use.
Methyl cyanodithioformate (1) is an electron-deficient thiocarbonyl compound2 that reacts readily with dienes to give dihydrothiopyran Diels-Alder adducts.3-5 The regiochemistry of these cycloadditions is opposite to that observed with electron-deficient carbonyl compounds. Reaction of 1-methoxy-1,3-butadiene with (1) at 0 °C for 1 h affords mainly dihydrothiopyran (2) in which the cyano group has added endo. Reaction of (2) with Osmium Tetroxide affords the carbohydrate analog (3) (eq 1).3d
Methyl cyanodithioformate undergoes ene reactions with excess alkene in toluene at 100-110 °C for 5-72 h, affording allylic sulfide ene adducts in 45-83% yield.6 A carbon-sulfur, rather than carbon-carbon, bond is formed in the ene reaction, as shown for b-pinene in eq 2. Treatment of the adduct (4) with Lithium Diisopropylamide or n-Butyllithium in THF/HMPA generates an anion that undergoes a [2,3]-sigmatropic rearrangement to give (5) after trapping with MeI. Reduction of (5) with deactivated W-4 Raney Nickel affords nitrile (6). This sequence provides a procedure for the insertion of a functionalized carbon into an allylic carbon-hydrogen bond.
Methyl cyanodithioformate undergoes condensation reactions with amines7 and dipolar cycloadditions followed by extensive rearrangements with triazolium imide 1,3-dipoles.8
Barry B. Snider
Brandeis University, Waltham, MA, USA