A Simple Synthesis of 2-Methyl-1,3-Dithiolium and Related Cations

Abstract

A simple, high-yielding synthesis of 2-methyl-1,3-dithiolium tetrafluoroborates is reported. The reaction of these salts with N,N-dimethylformamide and acetic anhydride gives rise to the previously unreported N,N-dimethyl 2-(1,3-dithiol-2-yliden)ethylideniminium tetrafluoroborates.

heterocycles - sulfur - 1,3-dithiolium cations - Meldrum’s acid

References and Notes

<A NAME="RD33106ST-1A">1a</A> Campaigne E. Hamilton RD. Q. Rep. Sulfur Chem.  1970,  5:  275 

<A NAME="RD33106ST-1B">1b</A> Lozac’h N. Stavaux M. Adv. Heterocycl. Chem.  1980,  27:  151 

<A NAME="RD33106ST-1C">1c</A> Schukat G. Fanghänel E. In Science of Synthesis   Vol. 11:  Schaumann E. Thieme; Stuttgart: 2002.  p.191 

<A NAME="RD33106ST-2A">2a</A> Garín J. Adv. Heterocycl. Chem.  1995,  62:  249 

<A NAME="RD33106ST-2B">2b</A> Schukat G. Fanghänel E. Sulfur Rep.  2003,  24:  1 

<A NAME="RD33106ST-2C">2c</A> Fabre JM. Chem. Rev.  2004,  104:  5133 

<A NAME="RD33106ST-3A">3a</A> Wizinger-Aust R. Q. Rep. Sulfur Chem.  1970,  5:  191 

<A NAME="RD33106ST-3B">3b</A> Mayer R. Fabian K. Kröber H. Hartmann H. J. Prakt. Chem.  1972,  314:  240 

<A NAME="RD33106ST-3C">3c</A> Kreitsberga YN. Vilyuma EV. Khodorkovskii VY. Neiland OY. Chem. Heterocycl. Comp. (Engl. Transl.)  1988,  1339 

<A NAME="RD33106ST-4A">4a</A> Appriou P. Guglielmetti R. Bull. Soc. Chim. Fr.  1974,  510 

<A NAME="RD33106ST-4B">4b</A> Minkin VI. Nivorozhkin LE. Trofimova NS. Revinskii YV. Knyazhanskii MI. Volbushko NV. Osipov OA. Lukash AV. Simkin BY. J. Org. Chem. USSR  1975,  11:  818 

<A NAME="RD33106ST-5">5</A> Simonsen KB. Geisler T. Petersen JC. Arentoft J. Sommer-Larsen P. Rodriguez Greve D. Jakobsen C. Becher J. Malagolid M. Brédas JL. Bjørnholm T. Eur. J. Org. Chem.  1998,  2747 

<A NAME="RD33106ST-6A">6a</A> Leaver D. Robertson WAH. McKinnon DM. J. Chem. Soc.  1962,  5104 

<A NAME="RD33106ST-6B">6b</A> Fabian K. Hartmann H. J. Prakt. Chem.  1971,  313:  722 

<A NAME="RD33106ST-7">7</A>

The perchlorate of cation 4c has been isolated.⁶ Cation 4b has only been generated in aqueous solution as its perchlorate salt^3c or isolated in low yield as the corresponding triiodide.^6b

<A NAME="RD33106ST-8A">8a</A>

Thione 1a is commercially available.

<A NAME="RD33106ST-8B">8b</A> Compounds 1b and 1c were prepared according to: Haley NF. Fichtner MW. J. Org. Chem.  1980,  45:  175 

<A NAME="RD33106ST-8C">8c</A> Compound 1d was prepared according to: Steimecke G. Sieler H.-J. Kirmse R. Hoyer E. Phosphorus Sulfur Relat. Elem.  1979,  7:  49 

<A NAME="RD33106ST-9A">9a</A> Compound 2a: Challenger F. Mason EA. Holdsworth EC. Emmott R. J. Chem. Soc.  1953,  292 

<A NAME="RD33106ST-9B">9b</A> Compounds 2b-d: Moore AJ. Bryce MR. Synthesis  1991,  26 

<A NAME="RD33106ST-10">10</A> McNab H. Chem. Soc. Rev.  1978,  7:  345 

<A NAME="RD33106ST-11">11</A>

Isopropylidene 1,3-Dithiol-2-ylidenemalonates 3 - General Procedure
To a solution of the corresponding salt 2 (10 mmol) and Meldrum’s acid (1.44 g, 10 mmol) in EtOH (15 mL; 30 mL for 2c), DIPEA (1.9 mL, 11 mmol) was added. The mixture was refluxed under Ar for 3 h and then allowed to cool to r.t. The resulting solid was filtered off and purified by recrystallization from EtOH or column chromatography (silica gel, CH₂Cl₂) in the case of 3c.

<A NAME="RD33106ST-12">12</A>

Some of these isopropylidene malonates had already been prepared under different conditions than those described here, but their reported melting points^3c are lower than those measured by us. Therefore, full characterization data for compounds 3 follow:
Compound 3a: yield 69%; mp 244-245 °C (lit.^3c 235-237 °C). IR (Nujol): 1651 cm^-1. ¹H NMR (400 MHz, DMSO-d ₆): δ = 7.97 (s, 2 H), 1.66 (s, 6 H). ¹³C NMR (100 MHz, DMSO-d ₆): δ = 182.0, 161.1, 128.4, 103.8, 93.4, 26.3. MS (EI): m/z (%) = 244 (60).
Compound 3b: yield 76%; mp 219-220 °C (lit.^3c 208-210 °C). IR (Nujol): 1665 cm^-1. ¹H NMR (300 MHz, CDCl₃): δ = 2.30 (s, 6 H), 1.70 (s, 6 H). ¹³C NMR (100 MHz, CDCl₃): δ = 179.4, 162.1, 132.7, 104.2, 93.4, 26.9, 13.1. MS (EI): m/z (%) = 272 (70).
Compound 3c: yield 68%; mp 202-203 °C. IR (Nujol): 1665 cm^-1. ¹H NMR (400 MHz, CDCl₃): δ = 7.62-7.60 (m, 2 H), 7.49-7.44 (m, 3 H), 7.43 (s, 1 H), 1.76 (s, 6 H). ¹³C NMR (100 MHz, CDCl₃): δ = 181.1, 161.8, 144.8, 130.4, 130.3, 129.5, 127.0, 119.6, 104.5, 94.5, 27.0. ESI-HRMS: m/z calcd for C₃₀H₂₄NaO₈S₄ [2 M + Na⁺]: 663.0246; found: 663.0222. HRMS: m/z calcd for C₁₅H₁₂NaO₄S₂ [M + Na⁺]: 343.0069; found: 343.0063.
Compound 3d: yield 56%; mp 194-195 °C (lit.^3c 187-189 °C). IR (Nujol): 1676 cm^-1. ¹H NMR (400 MHz, CDCl₃): δ = 2.57 (s, 6 H), 1.73 (s, 6 H). ¹³C NMR (100 MHz, CDCl₃): δ = 179.4, 161.6, 135.2, 104.6, 26.9, 19.2. MS (EI): m/z (%) = 336 (95).

<A NAME="RD33106ST-13A">13a</A> Wilt JR. Reynolds GA. Van Allan JA. Tetrahedron  1973,  29:  795 

<A NAME="RD33106ST-13B">13b</A> Weidner CH. Wadsworth DH. Bender SL. Beltman DJ. J. Org. Chem.  1989,  54:  3660 

<A NAME="RD33106ST-13C">13c</A> Yagi S. Maeda K. Nakazumi H. J. Mater. Chem.  1999,  9:  2991 

<A NAME="RD33106ST-14">14</A>

2-Methyl-1,3-Dithiolium Tetrafluoroborates 4 - General Procedure
To a solution of the corresponding compound 3 (2 mmol) in AcOH (10 mL; 20 mL for 3b and 3d), HBF₄ (54% in Et₂O, 4 mL) was added under Ar. The mixture was refluxed for 1 h and allowed to cool to r.t. Most of the AcOH was rotary evaporated and the resulting residue was slowly added to ice-cooled Et₂O (100 mL). The so formed solid was recovered by filtration, washed with Et₂O, dried, and optionally recrystallized from AcOH. In the case of 4d we have not been able to completely purify the desired salt.

<A NAME="RD33106ST-15">15</A>

Compound 4a: yield 82%; mp 109-110 °C. ¹H NMR (300 MHz, CF₃COOD): δ = 8.92 (s, 2 H), 3.43 (s, 3 H). ¹³C NMR (75 MHz, CF₃COOD): δ = 204.3, 145.1, 20.6. MS (MALDI, dithranol): m/z = 117 [C₄H₅S₂].
Compound 4b: yield 87%; mp 50-51 °C (dec.). ¹H NMR (300 MHz, CDCl₃): δ = 3.28 (s, 3 H), 2.69 (s, 6 H). ¹³C NMR (100 MHz, CDCl₃): δ = 193.9, 151.4, 19.5, 14.3. MS (MALDI, dithranol): m/z = 145 [C₆H₉S₂].
Compound 4c: yield 84%; mp 129-132 °C. ¹H NMR (300 MHz, CF₃COOD): δ = 8.73 (s, 1 H), 7.69-7.52 (m, 5 H), 3.40 (s, 3 H). ¹³C NMR (75 MHz, CF₃COOD): δ = 202.0, 135.9, 135.2, 132.6, 129.9, 20.6. MS (MALDI, dithranol): m/z = 193 [C₁₀H₉S₂].
Compound 4d: ¹H NMR (400 MHz, CDCl₃): δ = 3.32 (s, 3 H), 2.75 (s, 6 H). ¹³C NMR (100 MHz, CDCl₃): δ = 196.9, 151.8, 20.6, 19.9. MS (MALDI, dithranol): m/z = 209 [C₆H₉S₄].

N,N-Diethyliminium analogues of 5 have been prepared by the reaction of 2-alkylsulfanyl-1,3-dithiolium salts with I₂ and Et₃N:

<A NAME="RD33106ST-16A">16a</A> Wadsworth DH. Detty MR. Murray BJ. Weidner CH. Haley NF. J. Org. Chem.  1984,  49:  2676 

<A NAME="RD33106ST-16B">16b</A> Khodorkovskii VY. Veselova LN. Neiland OY. Chem. Heterocycl. Comp. (Engl. Transl.)  1990,  112 

<A NAME="RD33106ST-16C">16c</A> Leriche P. Roquet S. Pillerel N. Mabon G. Frère P. Tetrahedron Lett.  2003,  44:  1623 

<A NAME="RD33106ST-17">17</A> Frère P. Skabara PJ. Chem. Soc. Rev.  2005,  34:  69 

<A NAME="RD33106ST-18A">18a</A> Andreu R. Garín J. Orduna J. Alcalá R. Villacampa B. Org. Lett.  2003,  5:  3143 

<A NAME="RD33106ST-18B">18b</A> Andreu R. Blesa MJ. Carrasquer L. Garín J. Orduna J. Villacampa B. Alcalá R. Casado J. Ruiz Delgado MC. Lópe Navarrete JT. Allain M. J. Am. Chem. Soc.  2005,  127:  8835 

<A NAME="RD33106ST-19">19</A> Würthner F. Synthesis  1999,  2103 

<A NAME="RD33106ST-20">20</A>

N , N -Dimethyliminium Tetrafluoroborates 5 - General Procedure
To a solution of the corresponding salt 4 (0.86 mmol) in Ac₂O (10 mL), anhyd DMF (0.7 mL, 9 mmol) was added. The mixture was heated to 100 °C under Ar for 0.5 h, then allowed to cool to r.t., and finally poured into ice-cooled Et₂O (125 mL). The resulting solid was isolated by filtration, washed with Et₂O, dried, and recrystallized from AcOH if necessary.

<A NAME="RD33106ST-21">21</A>

Compound 5a: yield 59%; mp 161-162 °C. IR (Nujol): 1625 cm^-1. ¹H NMR (400 MHz, DMSO-d ₆): δ = 8.38 (d, 1 H, J = 11.8 Hz), 7.57 (s, 2 H), 6.91 (d, 1 H, J = 11.8 Hz), 3.41 (s, 3 H), 3.19 (s, 3 H). ¹³C NMR (100 MHz, DMSO-d ₆): δ = 181.9, 157.8, 125.8, 99.1, 46.4. MS-FAB: m/z = 172 [C₇H₁₀NS₂].
Compound 5b: yield 65%; mp 193-194 °C. IR (Nujol): 1630 cm^-1. ¹H NMR (300 MHz, DMSO-d ₆): δ = 8.33 (d, 1 H, J = 11.8 Hz), 6.84 (d, 1 H, J = 11.8 Hz), 3.40 (s, 3 H), 3.18 (s, 3 H), 2.23 (s, 6 H). ¹³C NMR (100 MHz, DMSO-d ₆): δ = 183.2, 162.6, 134.7, 104.1, 51.7, 44.3, 18.5, 18.1. MS (MALDI, dithranol): m/z = 200 [C₉H₁₄NS₂].
Compound 5c: yield 40%; mp 224 °C (dec.; darkening from 175 °C). IR (Nujol): 1626 cm^-1. ¹H NMR (400 MHz, DMSO-d ₆): δ = 8.49 (d, 0.5 H, J = 12.0 Hz), 8.46 (d, 0.5 H, J = 12.5 Hz), 7.89 (s, 1 H), 7.62-7.48 (m, 5 H), 7.02 (d, 0.5 H, J = 12.5 Hz), 6.98 (d, 0.5 H, J = 12.0 Hz), 3.45 (s, 3 H), 3.24 (s, 3 H). ¹³C NMR (100 MHz, DMSO-d ₆): δ = 178.5, 158.3, 158.0, 139.3, 139.1, 129.9, 129.8, 129.6, 129.5, 126.5, 126.4, 119.9, 119.2, 100.5, 100.2, 46.7, 39.3. MS (MALDI, dithranol): m/z = 248 [C₁₃H₁₄NS₂].

<A NAME="RD33106ST-22">22</A> Scheibe G. Seiffert W. Hohlneicher G. Jutz Ch. Springer HJ. Tetrahedron Lett.  1966,  7:  5053 

<A NAME="RD33106ST-23">23</A> Childs RF. Dickie BD. J. Am. Chem. Soc.  1983,  105:  5041 

<A NAME="RD33106ST-24">24</A> Poleschner H. Radeglia R. Phosphorus Sulfur Relat. Elem.  1987,  29:  187 

<A NAME="RD33106ST-25">25</A> Andreu R. Garín J. López C. Orduna J. Levillain E. Tetrahedron Lett.  2004,  45:  8211