Synlett 2018; 29(20): 2673-2678
DOI: 10.1055/s-0037-1610325
letter
© Georg Thieme Verlag Stuttgart · New York

Understanding Six-Membered NHC-Copper(I) Allylic Borylation Selectivity by Comparison with other Catalysts and Different Substrates

Minyoung Jo ◊
,
Daniel Rivalti ◊
,
Andrew R. Ehle
,
Alina Dragulescu-Andrasi
,
Manuel Hartweg
,
Michael Shatruk*
,
D. Tyler McQuade*
This work was supported by the National Science Foundation (grant CHE-1152020).
Further Information

Publication History

Received: 10 July 2018

Accepted after revision: 23 October 2018

Publication Date:
21 November 2018 (eFirst)

These authors contributed equally to this work

Abstract

We recently introduced a family of 6-NHC-Cu(I) catalysts that exhibit highest selectivities (regio- and enantio-) exclusively when aryl ethers are used as the leaving group. Understanding the match ­between a catalyst and leaving group remains elusive. We sought to increase our understanding of this system by comparing our catalyst’s ­activity with other catalysts using substrates that contain different leaving groups. Our objective is to better understand the regioselectivity–leaving group combinations. We also observed that our catalyst functioned best when methanol was used as an additive. We examined the selectivities as a function of other protic additives. Finally, we wanted to understand the regioselectivity–enantioselectivity relationship with regards to internal versus terminal leaving groups. Overall, we demonstrate that matching leaving group and catalyst is important and that for our extended aromatic ligand the use of aromatic leaving groups is a unique pairing. We also demonstrate that the leaving group is also critical for controlling both types of selectivity.

Supporting Information

 
  • References and Notes

  • 1 New address: Chemical and Life Science Engineering, Virginia Commonwealth University, Richmond, Virginia 23284, USA; tmcquade@vcu.edu.
    • 2a Egbert JD, Cazin CS. J, Nolan SP. Catal. Sci. Tech. 2013; 3: 912
    • 2b Lin JC. Y, Huang RT. W, Lee CS, Bhattacharyya A, Hwang WS, Lin IJ. B. Chem. Rev. 2009; 109: 3561
    • 2c Alexakis A, Backvall JE, Krause N, Pamies O, Dieguez M. Chem. Rev. 2008; 108: 2796
    • 2d Díez-González S, Marion N, Nolan SP. Chem. Rev. 2009; 109: 3612
    • 2e Diez-Gonzalez S, Nolan SP. Synlett 2007; 2158
    • 3a Gao F, Carr JL, Hoveyda AH. Angew. Chem. Int. Ed. 2012; 51: 6613
    • 3b Gao F, Carr JL, Hoveyda AH. J. Am. Chem. Soc. 2014; 136: 2149
    • 3c Shi Y, Hoveyda AH. Angew. Chem. Int. Ed. 2016; 55: 3455
    • 3d Shi Y, Jung B, Torker S, Hoveyda AH. J. Am. Chem. Soc. 2015; 137: 8948
    • 3e Harada A, Makida Y, Sato T, Ohmiya H, Sawamura M. J. Am. Chem. Soc. 2014; 136: 13932
    • 3f Yasuda Y, Ohmiya H, Sawamura M. Angew. Chem. Int. Ed. 2016; 55: 10816
    • 3g Meng FK, McGrath KP, Hoveyda AH. Nature 2014; 513: 367
    • 3h Jung B, Hoveyda AH. J. Am. Chem. Soc. 2012; 134: 1490
    • 3i Li XB, Meng FK, Torker S, Shi Y, Hoveyda AH. Angew. Chem. Int. Ed. 2016; 55: 9997
    • 4a Douthwaite RE. Coord. Chem. Rev. 2007; 251: 702
    • 4b Nakanishi M, Katayev D, Besnard C, Kundig EP. Angew. Chem. Int. Ed. 2011; 50: 7438
    • 4c Pace V, Rae JP, Procter DJ. Org. Lett. 2014; 16: 476
    • 4d Zhao DB, Candish L, Paul D, Glorius F. ACS Catal. 2016; 6: 5978
    • 5a Huang LL, Cao Y, Zhao MP, Tang ZF, Sun ZH. Org. Biomol. Chem. 2014; 12: 6554
    • 5b Lu WY, Cavell KJ, Wixey JS, Kariuki B. Organometallics 2011; 30: 5649
    • 5c Dunsford JJ, Cavell KJ, Kariuki BJ. Organomet. Chem. 2011; 696: 188
    • 5d Davies CJ. E, Page MJ, Ellul CE, Mahon MF, Whittlesey MK. Chem. Commun. 2010; 46: 5151
    • 5e Scarborough CC, Guzei IA, Stahl SS. Dalton Trans. 2009; 2284
    • 5f Scarborough CC, Bergant A, Sazama GT, Guzei IA, Spencer LC, Stahl SS. Tetrahedron 2009; 65: 5084
    • 5g Metallinos C, Du XD. Organometallics 2009; 28: 1233
    • 5h Kolychev EL, Portnyagin IA, Shuntikov VV, Khrustalev VN, Nechaev MS. J. Organomet. Chem. 2009; 694: 2454
    • 5i Binobaid A, Iglesias M, Beetstra DJ, Kariuki B, Dervisi A, Fallis IA, Cavell KJ. Dalton Trans. 2009; 7099
    • 5j Seo H, Hirsch-Weil D, Abboud KA, Hong S. J. Org. Chem. 2008; 73: 1983
    • 5k Baskakov D, Herrmann WA, Herdtweck E, Hoffmann SD. Organometallics 2007; 26: 626
  • 6 Park JK, Lackey HH, Ondrusek BA, McQuade DT. J. Am. Chem. Soc. 2011; 133: 2410
  • 7 Park JK, Lackey HH, Rexford MD, Kovnir K, Shatruk M, McQuade DT. Org. Lett. 2010; 12: 5008
  • 8 Park JK, Ondrusek BA, McQuade DT. Org. Lett. 2012; 14: 4790
  • 9 Park JK, McQuade DT. Angew. Chem. Int. Ed. 2012; 51: 2717
    • 10a Delvos LB, Vyas DJ, Oestreich M. Angew. Chem. Int. Ed. 2013; 52: 4650
    • 10b Delvos LB, Hensel A, Oestreich M. Synthesis 2014; 46: 2957
    • 10c Hensel A, Nagura K, Delvos LB, Oestreich M. Angew. Chem. Int. Ed. 2014; 53: 4964
    • 11a Park JK, McQuade DT. Synthesis 2012; 44: 1485
    • 11b Reviews of this manuscript offered an equally plausible mechanism whereby the rate-determining transition state includes a p-allyl-Cu(III) interaction (Figure 2).
    • 12a Yamanaka M, Kato S, Nakamura E. J. Am. Chem. Soc. 2004; 126: 6287
    • 12b Kim J, Park S, Park J, Cho SH. Angew. Chem. Int. Ed. 2016; 55: 1498
    • 12c Yoshikai N, Nakamura E. Chem. Rev. 2012; 112: 2339
    • 12d Bartholomew ER, Bertz SH, Cope S, Murphy M, Ogle CA. J. Am. Chem. Soc. 2008; 130: 11244
    • 12e Rideau E, You HZ, Sidera M, Claridge TD. W, Fletcher SP. J. Am. Chem. Soc. 2017; 139: 5614
  • 13 Opalka SM, Park JK, Longstreet AR, McQuade DT. Org. Lett. 2013; 15: 996
  • 14 General Procedure for Asymmetric Allylic Borylations Using the NHC-CuCl Catalysts in Table [1] NHC-copper catalyst (0.02 equiv, 0.004 mmol) was loaded into a flame-dried Schlenk tube. Anhydrous diethyl ether (0.1 mL) was added to the reaction tube, and the suspension was stirred and cooled to –50 °C. NaOtBu (0.3 equiv), MeOH (2 equiv), and bis(pinacolato)diboron (1.5 equiv) were added in order, and the reaction mixture was stirred for 10 min. Allyl ether (1 equiv, 0.2 mmol) was added, and the reaction mixture was stirred at –50 °C. The resulting mixture was filtered through short Celite pad and washed with diethyl ether. The filtrate was concentrated under reduced pressure. For the determination of regioselectivity, 1H NMR was measured with crude product. For the determination of enantioselectivity, the resulting crude material was dissolved in ethyl acetate (2 mL) and oxidized by treatment of H2O2 (5 equiv) and 1 M NaOH aqueous solution (2 equiv). After stirring for 1 h, the mixture was quenched by water. The organic layer was extracted with ethyl acetate and evaporated in vacuo. The crude alcohol product was separated by preparative TLC for the HPLC measurement. Branched Boronate Product 1H NMR (600 MHz, CDCl3): δ = 7.28–7.25 (m, 2 H), 7.19–7.15 (m, 3 H), 5.82 (ddd, J = 17.1, 10.2, 8.3 Hz, 1 H), 5.04–4.99 (m, 2 H), 2.68–2.63 (m, 1 H), 2.59-2.54 (m, 1H), 1.90–1.86 (m, 2 H), 1.76–1.72 (m, 1 H), 1.24 (s, 12 H) ppm. All the resonances in the spectra were in accordance with reported values. Linear Boronate Product 1H NMR (600 MHz, CDCl3): δ = 7.28–7.24 (m, 2 H), 7.21–7.15 (m, 3 H), 5.54–5.43 (m, 2 H), 2.66 (td, J = 7.8, 4.1 Hz, 2 H), 2.36–2.28 (m, 2 H), 1.65 (t, J = 7.0 Hz, 2 H), 1.24 (s, 12 H) ppm. All the resonances in the spectra were in accordance with reported values. Reduction Product 1H NMR (600 MHz, CDCl3): δ = 7.30–7.28 (m, 2 H), 7.21–7.18 (m, 3 H), 7.06 (t, J = 8.0 Hz, 1 H), 6.34 (dd, J = 8.2, 2.3 Hz, 1 H), 6.31 (dd, J = 7.8, 2.1 Hz, 1 H), 6.26 (s, 1 H), 5.90–5.84 (m, 1 H), 5.77–5.72 (m, 1 H), 4.43 (dd, J = 5.9, 1.3 Hz, 2 H), 2.73 (dd, J = 9.1, 6.7 Hz, 2 H), 2.49–2.36 (m, 2 H) ppm. 13C NMR (151 MHz, CDCl3): δ = 160.0, 156.6, 147.7, 141.8, 134.4, 130.3, 130.2, 128.5, 128.4, 126.0, 125.7, 122.0, 115.8, 110.6, 108.2, 105.1, 102.1, 68.6, 35.5, 34.2 ppm. HRMS-ESI: m/z calcd for [C17H19NO + H]+ : 254.1545; found: 254.1556.
  • 15 Lu HT, Geng ZY, Li JY, Zou DP, Wu YS, Wu YJ. Org. Lett. 2016; 18: 2774
  • 16 Mun S, Lee JE, Yun J. Org. Lett. 2006; 8: 4887
  • 17 Followed general reaction protocol in ref. 14 except that 1 mol% of NHC-Cu complex 4 was used. Reaction mixture was stirred at –50 °C for 16 h.