Catalyst-Free Visible-Light-Mediated Iodoamination of Olefins and Synthetic Applications
Sebastian Engl and Oliver Reiser*
*Institute of Organic Chemistry, University of Regensburg, 93053 Regensburg, Germany, Email: oliver.reiserchemie.uniregensburg.de
S. Engl, O. Reiser, Org. Lett., 2021, 23, 5581-5586.
DOI: 10.1021/acs.orglett.1c02035 (free Supporting Information)
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A catalyst- and metal-free visible-light-mediated protocol enables the iodoamination of miscellaneous olefins in high yields under environmentally benign reaction conditions using DMC as green and biodegradable solvent. Furthermore, the protocol allows for late-stage functionalization of bioactive molecules and can be scaled to gram quantities of product.
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All photochemical reactions were performed in flame-dried Schlenk tubes (10.0 mL size; D) equipped with a magnetic stirring bar (E) using a monochromatic light emitting diodes LED (A) as irradiation source. The LED is placed on a glass rod (8 mm diameter; borosilicate glass; Schott Borofloat® 33; B) as fiber optics, which is directly immersed in the reaction mixture.
General procedure for photochemical iodoamination of olefins
A flame-dried Schlenk tube equipped with a magnetic stirring bar was charged with amine (0.5 mmol, 1.0 equiv), NIS (112.5 mg, 0.5 mmol, 1.0 equiv) and dissolved in DMC (2.0 mL, 0.25 M), sealed with a screw-cap and subsequently degassed by three consecutive freeze-pump-thaw cycles. Afterwards alkene (indicated equivalents) was added under a slight nitrogen overpressure and the screw-cap was replaced with a Teflon sealed inlet for a glass rod, through which irradiation with a 530 nm high power LED took place from above while the reaction mixture was magnetically stirred in an aluminum block at room temperature for 2 h. The reaction was monitored by TLC. Afterwards the reaction mixture was concentrated in vacuo (water bath temperature of rotary evaporator should not exceed 40 °C) and the residue purified by flash column chromatography on silica gel.
Please note: Products are sensitive to heat. Also, slow decomposition is noticeable in solution if oxygen or acid is present. Column chromatography should be performed immediately, and the solvent evaporated as soon as possible. Isolated compounds can be stored neatly in the dark at 4 – 8 °C (fridge).