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Synlett 2014; 25(18): 2665-2668
DOI: 10.1055/s-0034-1379167
letter
© Georg Thieme Verlag Stuttgart · New York

A Late-Stage Strategy for the Functionalization of Triazolium-Based NHC Catalysts

Kerem E. Ozboya
Department of Chemistry, Colorado State University, Fort Collins, CO 80523, USA   Fax: +1(970)4911801   Email: rovis@lamar.colostate.edu
,
Tomislav Rovis*
Department of Chemistry, Colorado State University, Fort Collins, CO 80523, USA   Fax: +1(970)4911801   Email: rovis@lamar.colostate.edu
› Author Affiliations
Further Information

Publication History

Received: 29 July 2014

Accepted after revision: 27 August 2014

Publication Date:
18 September 2014 (online)

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Abstract

A strategy for the diversification of triazolium-based catalysts is presented. This method is based on the reduction to the triazoline, which serves as a suitable and stable substrate for palladium-mediated cross-coupling, followed by trityl cation mediated reoxidation to the triazolium.

Key words

NHC Catalysis - organocatalysis - asymmetric catalysis

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  • References and Notes

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  • 17 Typical Experimental Procedure – Synthesis of 5a In a glove box, a dry 2-dram glass vial was loaded with PdCl2(PPh3)2 (7 mg, 0.01 mmol, 0.05 equiv). The vial was sealed and removed from the glove box. To this vial was added triazoline (100 mg, 0.22 mmol, 1 equiv), phenylboronic acid (0.32 mmol, 1.5 equiv), and potassium phosphate tribasic (93 mg, 0.44 mmol, 2 equiv). Anhydrous THF (1.5 mL) was added followed by H2O (0.5 mL), as well as a magnetic stir bar. The vial was sealed, secured with Teflon tape, and heated by oil bath at 60 °C for 6 h. Reaction was deemed complete by TLC. The reaction was cooled to r.t. and brine (1 mL) and EtOAc (1 mL) was added to the reaction. The aqueous fraction was removed, and the organic layer was dried over MgSO4. The crude reaction product was filtered and concentrated. The crude product was purified by flash column chromatography, eluting with 0–50% EtOAc–hexanes through basic alumina, and 60 mg of dark brown solid was isolated (60% yield). Rf  = 0.5 (50% EtOAc–hexane). 1H NMR (300 MHz, acetone-d 6): δ = 7.70–7.60 (m, 4 H), 7.47–7.35 (m, 4 H), 5.68–5.67 (m, 1 H), 5.04 (t, J = 1.1 Hz, 1 H), 4.78 (dd, J = 5.6, 1.1 Hz, 1 H), 4.64–4.55 (m, 2 H), 4.47 (d, J = 15.6 Hz, 1 H), 3.30–3.28 (m, 2 H). 13C NMR (101 MHz, acetone-d 6): δ = 149.0, 141.6, 140.9, 140.3, 139.6, 129.82, 129.73, 128.49, 128.44, 128.38, 127.8, 127.25, 127.18, 127.16, 126.8, 125.6, 123.8, 123.2, 77.1, 73.6, 62.3, 59.2, 34.8. MS: m/z calcd for C24H16F5N3O: 457.4; found: 458.1 [M + H]. IR (neat): 2914, 1626, 1504, 1479, 1429, 1340, 1307, 1055, 1039, 977 cm–1. [α]D 23 –39.17 (c 2.4, acetone).