Synlett 2019; 30(10): 1194-1198
DOI: 10.1055/s-0037-1611725
cluster
© Georg Thieme Verlag Stuttgart · New York

A Flow Microreactor Approach to a Highly Efficient DielsAlder Reaction with an Electrogenerated o-Quinone

,
Hirona Yoshizawa
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Department of Environment and System Sciences, Yokohama National University, 79-7 Tokiwadai, Hodogaya-ku, Yokohama, Kanagawa 240-8501, Japan   Email: atobe@ynu.ac.jp
› Author Affiliations
This work was financially supported by the Grant-in-Aid for Scientific Research on Priority Areas (15H0584720).
Further Information

Publication History

Received: 13 December 2018

Accepted after revision: 22 January 2019

Publication Date:
13 February 2019 (eFirst)

Published as part of the Cluster Electrochemical Synthesis and Catalysis

Abstract

We have demonstrated a Diels–Alder reaction of an o-quinone generated in an electrochemical flow microreactor. In the flow microreactor system, 4-tert-butyl-o-benzoquinone was easily electrogenerated from 4-tert-butylpyrocatechol in the absence of chemical oxidants and then rapidly used, without decomposing, in a subsequent Diels–Adler reaction with various fulvenes to give the desired products efficiently.

Supporting Information

 
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  • 10 Electrochemical Reaction in a Batch-Type Reactor The reaction of 4-tert-butylpyrocatechol (1; 10 mM) with 6,6-dimethylfulvene (3; 200 mM) was performed by using a graphite plate anode (working electrode; 2 × 2 cm2) and a Pt plate cathode (counter-electrode, 2 × 2 cm2) in a 100 mM solution of NaClO4 in MeCN (10 mL). A constant current (1.5 mA cm–2) was applied during the electrolysis. After the electrolysis was complete, the mixture was analyzed by HPLC to determine the yield of the Diels–Alder cycloadduct 4. Electrochemical Reactions in the Flow Microreactor; General Procedure A 10 mM solution of 4-tert-butylpyrocatechol in a 100 mM solution of NaClO4 in MeCN was introduced into the reactor from a syringe pump (Model 100; KD Scientific, Holliston, MA: see Figs. S1 and S2 in the Supporting Information). Constant-current electrolysis was performed at 1.5 mA cm–2 by using the electrochemical flow microreactor. The electrolyzed solution emerging from the microreactor was poured into CH2Cl2 containing the appropriate fulvene (200 mM), and the mixture was stirred for 8 h. The mixture was then analyzed by HPLC to determine the yield of the Diels–Alder cycloadduct. (3aR*,4S*,7R*,7aS*)-6-(tert-Butyl)-1-(1-methylethylidene)-3a,4,7,7a-tetrahydro-1H-4,7-ethanoindene-8,9-dione (4) Yellow solid; yield: 75%; mp 97.7 °C. IR (KBr): 2964, 1732, 1508, 1473, 1458, 1363, 1099, 812 cm–1. 1H NMR (500 MHz, CDCl3): δ = 6.42 (dd, J = 5.7, 1.9 Hz, 1 H), 5.86 (ddd, J = 6.6, 2.2, 0.6 Hz, 1 H), 5.58 (dd, J = 5.7, 2.5 Hz, 1 H), 3.70 (dd, J = 3.0, 2.4 Hz, 1 H), 3.61 (dd, J = 6.8, 2.7 Hz, 1 H), 3.56 (d, J = 7.9 Hz, 1 H), 3.31 (d, J = 7.9 Hz, 1 H), 1.80 (s, 3 H), 1.77 (s, 3 H), 1.00 (s, 9 H). 13C NMR (126 MHz, CDCl3): δ = 191.5, 191.2, 151.8, 139.4, 135.6, 132.2, 125.2, 118.3, 54.1, 50.5, 46.4, 40.6, 35.3, 28.3, 21.7, 21.4. HRMS (ESI): m/z [M + Na]+ calcd for C18H22NaO2: 293.1512; found: 293.1498. (3aR*,4S*,7R*,7aS*)-6-tert-Butyl-1-(1-methylhexylidene)-3a,4,7,7a-tetrahydro-1H-4,7-ethanoindene-8,9-dione (6) Yellow solid; yield: 47%; mp 101.1 °C. IR (KBr): 2966, 2870, 1735, 1463, 1365, 1161, 813 cm–1. 1H NMR (500 MHz, CDCl3): δ = 6.44 (dd, J = 5.7, 1.9 Hz, 1 H), 5.84 (dd, J = 6.5, 2.1, 1 H), 5.60 (dd, J = 5.7, 2.5 Hz, 1 H), 3.69 (m, 1 H), 3.57 (dd, J = 6.8, 2.7 Hz, 1 H), 3.53 (m, 1 H), 3.34 (dd, J = 7.9, 2.5 Hz, 1 H), 2.10 (q, J = 7.04 Hz, 4 H), 1.48–1.55 (m, 1 H), 1.30–1.46 (m, 3 H) 1.00 (s, 9 H), 0.95 (t, J = 7.41 Hz, 3 H), 0.86 (t, J = 7.41 Hz, 3 H). 13C NMR (126 MHz, CDCl3): δ = 191.2, 191.2, 151.6, 139.9, 135.5, 134.0, 132.3, 118.1, 53.8, 51.1, 46.0, 40.0, 35.0, 34.5, 33.9, 28.1, 22.1, 21.6, 14.2, 13.9. HRMS (ESI) m/z [M + H]+ calcd for C22H31O2; 327.2309; found: 327.2319.
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