Nicholas Reactions of Alkynyl- and Alkenyltrifluoroborates

This paper is dedicated to Prof. Victor Snieckus, in consideration of his many years of mentorship and friendship, and for his tireless and continuing dedication to progress in synthetic aromatic chemistry

Abstract

The Lewis acid mediated Nicholas reaction of potassium alkynyltrifluoroborates and propargyl acetate-hexacarbonyldicobalt complexes affords 1,4-diyne dicobalt hexacarbonyl complexes in good yields. The analogous Nicholas reactions of potassium alkenyltrifluoro­borates give 1,3-enyne dicobalt hexacarbonyl complexes in most cases, although the initial site of reaction can vary. Potassium vinyltrifluoroborate itself affords alkynylcyclopropane complexes.

Key words

alkyne complexes - boron - carbocation - coupling - Lewis acids - alkynes - enynes

• References and Notes

• 1a Kann N. Curr. Org. Chem. 2012; 16: 322
• 1b Shea KM. In Name Reactions for Homologations . Li JJ. Wiley; Hoboken: 2009. Part 1 284
• 1c Diaz DD. Betancort JM. Martín VS. Synlett 2007; 343
• 1d Teobald BJ. Tetrahedron 2002; 58: 4133
• 1e Green JR. Curr. Org. Chem. 2001; 5: 809
• 1f Green, J. R.; Nicholas, K. M. Org. React., submitted for publication.
• 2a Padmanabhan S. Nicholas KM. J. Organomet. Chem. 1981; 212: 115
• 2b Padmanabhan S. Nicholas KM. Tetrahedron Lett. 1983; 24: 2239

For the use of alkynylaluminums, see:
• 3a Zweifel G. Miller JA. Org. React. 1984; 32: 375
• 3b Oishi M. In Science of Synthesis . Vol. 7. Yamamoto H. Thieme; Stuttgart: 2004: 261
• 3c Kessabi J. Beaudegnies R. Jung PM. J. Martin B. Montel F. Wendeborn S. Synthesis 2008; 655
• 4a Krafft ME. Cheung YY. Wright C. Cali R. J. Org. Chem. 1996; 61: 3912
• 4b Amiralaei S. Gauld J. Green JR. Chem. Eur. J. 2011; 17: 4157

There is greater consistent success in intramolecular reactions with alkenes, see:
• 5a Nakamura T. Matsui T. Tanino K. Kuwajima I. J. Org. Chem. 1997; 62: 3032
• 5b Mann A. Muller C. Tyrrell E. J. Chem. Soc., Perkin Trans. 1 1998; 1427
• 5c Lu Y. Green JR. Synlett 2001; 243
• 6a Molander GA. Jean-Gérard L. Org. React. 2013; 79: 1
• 6b Molander GA. Jean-Gérard L. In Boronic Acids, Hall D. G. Wiley-VCH; Weinheim: 2011. 2nd ed., Vol. 2, 507
• 6c Molander GA. Canturk B. Angew. Chem. Int. Ed. 2009; 48: 9240
• 6d Darses S. Genet J.-P. Chem. Rev. 2008; 108: 288
• 6e Molander GA. Ellis N. Acc. Chem. Res. 2007; 40: 275
• 6f Stefani HA. Cella R. Vieira AS. Tetrahedron 2007; 63: 3623

For use in conjugate additions, see:
• 7a Sanchez-Sancho F. Csaky AG. Synthesis 2016; 48: 2165
• 7b Koike T. Akita M. Org. Biomol. Chem. 2016; 14: 6886
• 8a Mitchell TA. Bode JW. J. Am. Chem. Soc. 2009; 131: 18057
• 8b Zeng J. Vedachalam S. Xiang S. Liu X.-W. Org. Lett. 2011; 13: 42
• 8c Vo C.-VV. Mitchell TA. Bode JW. J. Am. Chem. Soc. 2011; 133: 14082
• 8d Taylor C. Bolshan Y. Org. Lett. 2014; 16: 488
• 8e Fisher KM. Bolshan Y. J. Org. Chem. 2015; 80: 12676
• 8f Tatina MB. Hussain A. Dhas AK. Mukherjee D. RSC Adv. 2016; 6: 75960
• 8g Batey RA. Thadani AN. Smil DV. Lough AJ. Synthesis 2000; 990
• 8h Nakamura H. Yamamoto H. WO 2005043630, 2005 , Chem. Abstr. 2005, 142, 440277.
• 9 Experimental ProcedureTo a solution of 3a (89.7 mg, 0.218 mmol) and 2a (0.113 g, 0.544 mmol) in CH₂Cl₂ (8 mL) at 0 °C was added BF₃·OEt₂ (67 μL, 0.54 mmol). After 1.5 h at 0 °C, sat. NH₄Cl (aq) was added and the mixture subjected to conventional extractive workup (CH₂Cl₂). Flash chromatography (PE–Et₂O, 50:1) afforded 4aa (90.3 mg, 91%) as a viscous red oil.
• 10 Representative Characterization DataCompound 4aa: ¹H NMR (CDCl₃, 300 MHz): δ = 7.30–7.44 (m, 5 H), 4.00 (s, 2 H), 2.92 (q, J = 7.3 Hz, 2 H), 1.35 (t, J = 7.3 Hz, 3 H). ¹³C NMR (CDCl₃, 75 MHz): δ = 199.7, 131.5, 128.3, 128.0, 123.3, 101.6, 93.7, 86.5, 82.3, 26.9, 25.0, 15.6. IR: ν_max = 2971, 2088, 2043, 1989, 1600, 1490 cm^–1. HRMS: m/e calcd for C₁₉H₁₂Co₂O₆ [M⁺ – CO + H]: 454.9376; found: 454.9367.Compound 4ba: ¹H NMR (CDCl₃, 300 MHz): δ = 3.72 (t, J = 2.3 Hz, 2 H), 2.87 (q, J = 7.4 Hz, 2 H), 2.17 (m, 2 H), 1.31 (t, J = 7.4 Hz, 3 H), 0.90 (t, J = 7.1 Hz, 3 H). ¹³C NMR (CDCl₃, 75 MHz): δ = 200.0, 101.5, 95.3, 82.6, 76.7, 30.6, 26.8, 24.3, 21.9, 18.3, 15.5, 13.5. IR: ν_max = 2964, 2874, 2087, 2043, 1990, 1457. HRMS: m/e calcd for C₁₇H₁₆Co₂O₆ [M⁺ – CO + H]: 406.9740; found: 406.9733.Compound 4ca: ¹H NMR (CDCl₃, 300 MHz): δ = 3.76 (d, J = 2.6 Hz, 2 H), 2.88 (q, J = 7.4 Hz, 2 H), 2.19 (t, J = 2.6 Hz, 1 H), 1.32 (t, J = 7.4 Hz, 3 H). ¹³C NMR (CDCl₃, 75 MHz): δ = 200.2, 128.7, 128.0, 101.3, 98.9, 37.0, 27.1, 17.5, 15.6. IR: ν_max = 3314, 2972, 2877, 2089, 2044, 1994 cm^–1. HRMS: m/e calcd for C₁₃H₈Co₂O₆ [M⁺ + H]: 378.9063; found: 378.9063.
• 11 Nicholas reactions for γ-carbonyl cation equivalents routinely give more rapid reaction with Bu₂BOTf as Lewis acid relative to BF₃·OEt₂. See: Taj R. Green JR. J. Org. Chem. 2010; 75: 8258
• 12 Representative Characterization Data for Compound 7ab ¹H NMR (CDCl₃, 300 MHz): δ = 7.29–7.44 (m, 5 H), 6.61 (d, J = 15.7 Hz, 1 H), 6.31–6.41 (dt, J = 15.7, 7.2 Hz, 1 H), 3.77–3.79 (d, J = 7.2 Hz, 2 H), 2.92 (t, J = 7.6 Hz, 2 H), 1.48–1.77 (m, 4 H), 1.00 (t, J = 7.2 Hz, 3 H). ¹³C NMR (CDCl₃, 75 MHz): δ = 200.3, 137.0, 132.3, 128.6, 127.5, 127.4, 126.2, 99.4, 97.7, 37.4, 33.8, 22.8, 13.9. IR: ν_max = 3084, 3062, 3028, 2960, 2874, 2085, 2040, 1994, 1495 cm^–1. HRMS: m/e calcd for C₂₁H₁₈Co₂O₆ [M⁺ – CO + H]: 456.9896; found: 456.9907.
• 13 Representative Characterization DataCompound ( Z )-7bc: ¹H NMR (CDCl₃, 300 MHz): δ = 5.50–5.67 (m, 2 H), 3.68 (d, J = 6.7 Hz, 2 H), 1.70 (d, J = 5.9 Hz, 3 H), 0.31 (s, 9 H); resonances from the minor isomer were observed at δ = 3.56 (d, J = 5.9 Hz, 2 H), 0.30 (s, 9 H).¹³C NMR (CDCl₃, 75 MHz): δ (major isomer only) = 200.4, 128.0, 125.9, 111.2, 78.7, 32.3, 12.9, 0.6. IR: ν_max = 3025, 2959, 2984, 2085, 2041, 2000, 1581. HRMS: m/e calcd for C₁₅H₁₆Co₂O₆Si [M⁺ – CO + H]: 410.9509; found: 410.9501.Compound 8db: ¹H NMR (CDCl₃, 300 MHz): δ = 2.78 (t, J = 8.0 Hz, 2 H), 2.15 (tt, J = 7.4, 4.2 Hz, 1 H), 1.43–1.67 (m , 4 H), 1.11 (ddd, J = 7.4, 6.6, 4.3 Hz, 2 H), 0.97 (t, J = 7.2 Hz, 3 H), 0.72–0.77 (ddd, J = 6.6, 4.3, 4.2 Hz, 2 H). ¹³C NMR (CDCl₃, 75 MHz): δ = 200.1, 103.8, 98.4, 33.9, 33.6, 22.7, 15.2, 13.8, 12.5. IR: ν_max = 2962, 2876, 2086, 2040, 2005, 1450 cm^–1. HRMS: m/e calcd for C₁₆H₁₄Co₂O₆ [M⁺ – CO + H]: 380.9583; found: 380.9589.
• 14 Experimental ProcedureComplex 4bd (47.6 mg, 0.110 mmol) was dissolved in acetone (8 mL) and the solution cooled to –78 °C. CAN (0.302 g, 0.551 mmol, 5 equiv) was added and the solution allowed to warm to –30 °C (2 h), with monitoring by TLC. A sat. NaCl solution was added and the mixture subjected to a conventional extractive workup (Et₂O). The product was filtered through a silica plug using Et₂O and concentrated under reduced pressure to give 9bd (13.9 mg, 86%).
• 15a Bir G. Schacht W. Kaufmann D. J. Organomet. Chem. 1988; 340: 267
• 15b Vedejs E. Chapman RW. Fields SC. Lin S. Schrimpf MR. J. Org. Chem. 1995; 60: 3020
• 15c For a comparison of BF₃·OEt₂ with other common Lewis acids in aldehyde-allyltrifluoroborate reactions, see ref. 8g.
• 16 Our operating hypothesis for the predominant Z-isomer formation comes from the proposed larger size of the BF₃ ^– unit relative to a methyl group. Initial reaction consequently gives a cation 11 with the methyl nearly eclipsed to the homopropargyl-Co₂(CO)₆ unit (Scheme 4); subsequent hydride migration then gives a cation 12 where rotation of the C–B bond to a colinear orientation relative to the empty p-orbital of the cation is of lower energy than a rotation of the methyl group anti to the homopropargyl-Co₂(CO)₆ group.
• 17a Corey EJ. Lallic G. Tetrahedron Lett. 2008; 49: 4894
• 17b Zhang Y. Fu Z. Wang J. Li J. Chen S. Wei Y. Yu L. Tao X. WO 2016045587, 2016 , Chem. Abstr. 2016, 164, 438142.
• 18 For analogous reactivity of vinylsilanes with more electrophilic carbocations, see: Laub HA. Mayr H. Chem. Eur. J. 2014; 20: 1103
• 19 El-Amouri H. Gruselle M. Jaouen G. Daran JC. Vaissermann J. Inorg. Chem. 1990; 29: 3238