A new, mild one-pot synthesis of iodinated heterocycles as suitable precursors for N-heterocyclic carbene complexes

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Supporting Information

belonging to

A New, Mild, One-Pot Route to the Synthesis of Iodinated Heterocycles as suitable precursors for NHC complexes.

Manuel Iglesias, Oliver Schuster, and Martin Albrecht*

School of Chemistry and Chemical Biology, University College Dublin, Belfield, Dublin 4, Ireland.

E-mail: martin.albrecht@ucd.ie; Fax: (+)353-17162501.

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General comments. CH2Cl2 was dried by passage through solvent purification columns. All other reagents were commercially available and were used as received.

All ¹H and ¹³C{¹H}NMR spectra were recorded on Bruker Advance spectrometers, chemical shifts (d) are given in ppm and were referenced to residual solvent ¹H and

13C resonances (coupling constants J in Hz). Assignments are based either on distortionless enhancement of polarization transfer (DEPT) experiments or on homo- and heteronuclear shift correlation spectroscopy. Unless otherwise stated, all compounds were synthesized on a 5 mmol scale according to the typical procedure reported in reference 10 for the synthesis of compound 2c. The analytical data for 2f,^S1 2g,^S2 3e,^S3 and 3f^S4 were identical to the reported data.^S1–S4

Spectroscopic data for compound 2a: ¹H NMR (360 MHz, CDCl3): d 2.38 (s, CH3), 2.21 (s, CH3). ¹³C NMR (100 MHz, CDCl3): d 146.0 (s, NCN), 130.4 (bs, CCH₃, CI), 14.2 (s, CH₃), 11.4 (s, CH₃). Anal. Calcd for C₅H₄IN₂ (222.03): C, 27.05; H, 2.94; N, 12.33. Found: C, 26.90; H, 2.94; N, 12.36.

ESI-MS: 222.90 (100%)

Spectroscopic data for compound 2d: ¹H NMR (400 MHz, CDCl3): d 4.08 (q, NCH2CH3, ³JHH = 7.2), 2.27 (s, CH3), 2.21 (s, CH3), 1.36 (t, CH2CH3,

3J_HH = 7.2). ¹³C NMR (100 MHz, CDCl₃): d 145.0 (s, CCH₃), 139.7 (s, CCH₃), 62.3 (s, CI), 45.0 (s, NCH₂CH₃), 15.5 (s, CH₃), 14.0 (s, CH₃), 11.8 (s, NCH2CH3). Anal. Calcd for C5H7IN2 (250.0801): C, 33.62; H, 4.43; N, 11.20. Found: C, 33.51; H, 4.44; N, 11.04. ESI-MS: 251.0 (100%)

The final reaction mixture was comprised of two main products, which were. After separated by flash chromatography using Et₂O as eluent, thus affording 1-methyl-2-iodoimidazol (2f; rf = 0.5) and 1- methyl-4,5-diodoimidazol (3f; rf = 0.9) in 46% and 30%

yield, respectively. Analytical data are identical to those published previously.^S1,S4

N N I

2d N H N

2a I

N N

I

N N

I +

2f I 3f

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Synthesis of 2g: 2-Bromo-3-methylpyridine (4 mmol, 0.45 mL) was stirred with chlorotrimethylsylane (4.4 mmol, 0.6 mL, 1.1 equivalents) and sodium iodide (20 mmol, 3 g, 5 equivalents) in 15 mL of acetonitrile at 95 ºC for 10 days. The resulting solution was poured into a mixture of a 2M solution of sodium hydroxide (15 mL) and ca. 15 g of ice. The aqueous phase was extracted with diethyl ether (3 x 30 mL). The combined organic layers were washed with brine (20 mL), dried and the solvent evaporated under reduced pressure to afford the title compound as a yellow oil (570 mg, 2.6 mmol, 65%). Analytical data are identical to those published previously.^S2

References

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S2 Traylor, T. G.; Hill, K. W.; Tian, Z. Q.; Rheingold, A. L.; Peeisach, J.;

McCracken, J. J. Am. Chem. Soc. 1988, 110, 5571.

S3 Garden, S. J.; Torres, J. C.; de Souza Melo, S. C.; Lima, A. S.; Pinto, A. C.;

Lima, E. L. S. Tetrahedron Lett. 2001, 42, 2089.

S4 Holden, K. G.; Mattson, M. N.; Cha, K. H.; Rapoport, H. J. Org. Chem. 2002, 67, 5913.

2g N I