Synlett 2017; 28(19): 2569-2572
DOI: 10.1055/s-0036-1589093
cluster
© Georg Thieme Verlag Stuttgart · New York

Rhodium-Catalyzed Reductive Cleavage of Aryl Carbamates Using Isopropanol as a Reductant

Kosuke Yasui, Masaya Higashino, Naoto Chatani*, Mamoru Tobisu*
This work was supported by ACT-C (JPMJCR12ZF) from JST, Japan and Scientific Research on Innovative Area ‘Precisely Designed Catalysts with Customized Scaffolding’ (16H01022) from MEXT, Japan. K.Y. thanks JSPS Research Fellowship for Young Scientists.
Further Information

Publication History

Received: 31 May 2017

Accepted after revision: 10 July 2017

Publication Date:
17 August 2017 (eFirst)

Published as part of the Cluster C–O Activation

Abstract

Despite the widespread use of carbamates as a directing group in C–H bond-functionalization reactions, reductive removal of this directing group is not straightforward. Currently available methods are limited to nickel-catalyzed reactions using i PrMgX or hydrosilane as a reductant, leaving the functional group compatibility issue to be solved. Herein, we report rhodium-catalyzed reductive cleavage of aryl carbamates using iPrOH as a milder reductant.

Supporting Information

 
  • References and Notes


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  • 11 The reaction afforded an inseparable mixture of desired stilbene and 1,2-diphenylethane in a ratio of 82:18 (96% combined isolated yield).
  • 12 [6-(Pyridin-3-yl)naphthalen-2-yl](3,4,5-trimethoxyphenyl)methanone (2l); Typical Procedure [RhCl(C2H4)2]2 (5.8 mg, 0.015 mmol), L2·HCl (21 mg, 0.060 mmol), KO t Bu (7.4 mg, 0.066 mmol), K3PO4 (64 mg, 0.60 mmol), and toluene (0.40 mL) were added to a 5 mL screw-capped vial in a glovebox filled with nitrogen, and the resulting mixture was stirred at 60 °C for 1 h. After 1 h, 1l (154 mg, 0.30 mmol), i PrOH (18 mg, 0.30 mmol) and toluene (0.60 mL) were added to the vial in the glove box. The vessel was stirred at 180 °C for 16 h followed by cooling to room temperature. The mixture was purified by flash column chromatography over silica gel (eluting with hexane/EtOAc, 100:1) to give 2l as a white solid (90 mg, 75%); Rf 0.33 (EtOAc); pale-orange oil. 1H NMR (CDCl3, 400 MHz): δ = 9.02 (br. s, 1 H), 8.68 (br. s, 1 H), 8.33 (s, 1 H), 8.13 (s, 1 H), 7.96–8.07 (m, 4 H), 7.81 (d, J = 8.2 Hz, 1 H), 7.46 (br. s, 1 H), 7.14 (s, 2 H), 3.97 (s, 3 H), 3.89 (s, 6 H). 13C NMR (CDCl3, 100 MHz): δ = 195.5, 152.9, 149.0, 148.6, 142.2, 137.6, 136.0, 135.5, 135.3, 134.6, 132.7, 131.7, 131.1, 130.3, 128.5, 126.6, 126.1, 126.0, 123.7, 107.8, 61.0, 56. 3. IR (ATR): 2939 (w), 1715 (w), 1652 (w), 1626 (w), 1581 (m), 1503 (m), 1464 (m), 1413 (m), 1378 (w), 1328 (s), 1275 (w), 1234 (m), 1215 (m), 1171 (m), 1124 (s), 1001 (m), 912 (m), 823 (w), 801 (w), 750 (m), 726 (s), 645 (w) cm–1; HRMS (EI): m/z calcd for C25H21NO4: 399.1471; found: 399.1470.