[3,3]-Rearrangements of N-Oxyindoles

Abstract

The concerted Ag-catalyzed rearrangement of N-indolyl carbonates and esters to afford 3-oxyindole derivatives with broad functional-group compatibility is presented. In addition, this concerted [3,3]-rearrangement approach was expanded to the synthesis of phosphonate and sulfonamide derivatives without the use of an Ag catalyst. Control experiments suggested that no radical pathway is involved at any stage of the rearrangement process.

Key words

silver triflate - oxyindoles - rearrangement - indolyl carbonates - indolyl esters

• References and Notes

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• 14 The reaction products were analyzed by GC-MS spectrometry. Please see the Supporting Information for details.
• 15 Represented procedure: Synthesis of ethyl (2-phenyl-1H-indol-3-yl) carbonate (2a); An oven-dried An oven-dried 10-mL resealable reaction tube equipped with a stirrer bar was charged with carbonate 1a (56 mg, 0.2 mmol) and AgOTf (10 mol%, 5 mg). The tube was then evacuated and refilled with argon twice. DCE (0.1 M, 2 mL) was added under an argon counterflow, and the mixture was stirred at 40 °C until the reaction was complete (TLC, ~12 h). The crude mixture was concentrated under reduced pressure and purified by flash column chromatography [silica gel, hexanes–EtOAc (4:1)] to give a yellowish liquid 2a, yield: 44 mg (79%). ¹H NMR (600 MHz, CDCl₃): δ = 8.02 (br s, 1 H), 7.67 (dd, J = 8.4, 1.1 Hz, 2 H), 7.50 (dd, J = 7.9, 1.0 Hz, 1 H), 7.46 (dd, J = 8.4, 7.8 Hz, 2 H), 7.34 (tt, J = 7.8, 1.1 Hz, 1 H), 7.33 (dd, J = 8.0, 1.0 Hz, 1 H), 7.21 (ddd, J = 8.0, 7.2, 1.0 Hz, 1 H), 7.15 (ddd, J = 7.9, 7.2, 1.0 Hz, 1 H), 4.34 (q, J = 7.1 Hz, 2 H), 1.39 (t, J = 7.1 Hz, 3 H). ¹³C NMR (151 MHz, CDCl₃): δ = 153.8, 133.6, 130.6, 129.3, 128.1, 127.9, 126.4, 126.3, 123.4, 122.2, 120.8, 117.8, 111.6, 65.4, 14.5.