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Synlett 2018; 29(08): 1055-1060
DOI: 10.1055/s-0036-1591549
letter
© Georg Thieme Verlag Stuttgart · New York

PdII-Porphyrin Complexes – the First Use as Safer and Efficient Catalysts for Miyaura Borylation

Kanusu Umamaheswara Rao
a   Department of Chemistry, Jawaharlal Nehru Technological University Hyderabad, Kukatpally, Hyderabad 500 085, India
,
Katta Venkateswarlu  *
b   Laboratory for Synthetic & Natural Products Chemistry, Department of Chemistry, Yogi Vemana University, Kadapa 516 003, India   Email: kvenkat@yogivemanauniversity.ac.in
› Author AffiliationsAuthors are highly thankful to CSIR, New Delhi for financial support via Extramural Research Scheme, No. 02(0196)/14/EMR-II.
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Publication History

Received: 09 December 2017

Accepted after revision: 11 February 2018

Publication Date:
16 March 2018 (online)

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Abstract

We have developed a simple and convenient procedure for the preparation of pinacol arylboronates from aryl/heteroaryl bromides and bis(pinacolato)diborane using a PdII-porphyrin complex as a catalyst. Seven different PdII-porphyrin complexes (PdII-TmHPP, PdII-TmCPP, PdII-TPP, PdII-TSTpSPP, PdII-TpCPP, PdII-TpTP, and PdII-TpAP) have been synthesized and investigated for their catalytic influence in the Miyaura borylation.

Key words

Miyaura borylation - PdII-porphyrin complex - pinacol arylboronates

Supporting Information

    Supporting information for this article is available online at https://doi.org/10.1055/s-0036-1591549.
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  • References and Notes

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  • 15 General Procedure for Miyaura Borylation Aryl/heteroaryl bromide 1 (1 mmol), B2pin2(2), B2npg2(4) or Bpin (6, 1.2 mmol), and dioxane (5 mL) are taken into a 25 mL round-bottomed flask. KOAc (2 mmol) was added and stirred the resultant mixture at room temperature for 5 min, PdII-TpTP (0.15 mol%) was added, and the contents were refluxed on preheated oil bath at 110 °C under constant stirring in open-air. The reaction progress was ensured by TLC. After completion of the reaction, the mixture was cooled, dilute with water (20 mL) and extracted with tert butylmethyl ether (3 × 10 mL). The combined n-hexane layers were concentrated, and the crude product obtained was purified by column chromatography (CC) on silica gel using a mixture of ethyl acetate and hexane (1:30) as eluent. The structure of all the products were characterized by their spectral (1H NMR, 13C NMR and mass) analysis and are in good agreement with the literature data. Spectral data of some representative compounds are given below. Pinacol ( tert Butyl 4-carboxyphenyl)boronate (3b) White color solid; 85% (258 mg) yield. 1H NMR (DMSO-d 6, 300 MHz): δ = 7.90 (d, J = 8.4 Hz, 2 H), 7.78 (d, J = 8.4 Hz, 2 H), 1.55 (s, 9 H), 1.31 (s, 12 H) ppm. 13C NMR (DMSO-d 6, 75 MHz): δ = 164.8, 134.5, 133.7, 128.2, 84.1, 81.0, 27.8, 24.7 ppm. GC-MS: m/z = 304.2 [M+•]. Pinacol 4-Ethylphenylboronate (3j) Colorless liquid; 73% (169 mg) yield. 1H NMR (CDCl3, 300 MHz): δ = 7.74 (d, J = 7.8 Hz, 2 H), 7.21 (d, J = 7.8 Hz, 2 H), 2.66 (q, J = 7.5 Hz, 2 H), 1.33 (s, 12 H), 1.23 (t, J = 7.8 Hz, 2 H) ppm. 13C NMR (CDCl3, 75 MHz): δ = 147.7, 134.9, 127.4, 83.6, 29.1, 24.9, 15.5 ppm. GC-MS: m/z = 232.2 [M+•]. Pinacol 2-Fluoro-4-anisylboronate (3r) Colorless solid; 70% (176 mg) yield. 1H NMR (DMSO-d 6, 300 MHz): δ = 7.47 (dd, J = 7.8, 1.2 Hz, 1 H), 7.34 (dd, J = 12.0, 1.5 Hz, 1 H), 7.18 (t, J = 8.4 Hz, 1 H), 3.87 (s, 3 H), 1.28 (s, 12 H) ppm. 13C NMR (DMSO-d 6, 75 MHz): δ = 150.9 (d, J = 244.8 Hz), 149.6 (d, J = 10.3 Hz), 131.4 (d, J = 3.4 Hz), 120.4 (d, J = 15.7 Hz), 113.1, 83.4, 55.6, 24.3 ppm. GC-MS: m/z = 252.0 [M+•]. Pinacol 6-Chloro-2-pyridinylboronate (3r) 18 Colorless crystalline solid; 31% (74 mg) yield. 1H NMR (DMSO-d 6, 300 MHz): δ = 8.48 (dd, J = 4.8, 2.1 Hz, 1 H), 8.04 (dd, J = 7.5, 2.1 Hz, 1 H), 7.42 (dd, J = 7.5, 4.8 Hz, 1 H), 1.33 (s, 12 H) ppm. GC-MS: m/z = 239.0 [M+•].
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  • 17 Procedure for Miyaura Borylation – Suzuki–Miyaura Coupling After completion of the progress of the Miyaura borylation reaction (as indicated by the TLC and as given in Table 3) of aryl bromide 1d or 1f was added separately to each, 1m (1.2 mmol) and K2CO3 (2 mmol). The reactions are conducted at 110 °C and after completion the reaction mixture was cooled to room temperature, diluted by adding 20 mL water, and extracted with tertbutylmethyl ether (3 × 10 mL). The combined ether portions are evaporated in vacuo, and the crude product obtained was purified by CC by using a mixture of n-hexane and ethyl acetate (19:1) as eluent. The products were characterized by 1H NMR and 13C NMR spectroscopic, and mass spectrometric data and are in good agreement with our recent report.13a
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