Synthesis of Alkynylselenides under Visible-Light Irradiation Using the Ionic Liquid [BMIm]BF<sub>4</sub> as a Solvent

In this work, a visible-light-driven synthesis of alkynyl selenides using [BMIm]BF₄ as an environmentally friendly solvent and without the addition of metal catalysts, photosensitizers, directing-groups, or bases is reported. The target compounds were obtained in moderate to good yields with good functional group tolerance by the reaction of diorganoyldiselenides with 1-bromoalkynes proceeding through a radical mechanism.

Keywords:
ionic liquids; environmentally friendly synthesis; visible-light; organochalcogen

Authorship

Eduardo G. O. Soares

Instituto de Química, Universidade Federal do Rio Grande do Sul (UFRGS), PO Box 15003, 91501-970 Porto Alegre-RS, BrazilUniversidade Federal do Rio Grande do Sul (UFRGS)BrazilPorto Alegre, RS, BrazilInstituto de Química, Universidade Federal do Rio Grande do Sul (UFRGS), PO Box 15003, 91501-970 Porto Alegre-RS, Brazil

Douglas B. Paixão

Caren D. G. da Silva

Paulo H. Schneider ^** e-mail: paulos@iq.ufrgs.br

https://orcid.org/0000-0003-4082-7152

* e-mail: paulos@iq.ufrgs.br

Editor handled this article: Brenno A. D. Neto (Associate)

SCIMAGO INSTITUTIONS RANKINGS

Figures | Tables

Figures (5)
Tables (1)

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Scheme 1
Selected synthetic applications of alkynyl chalcogenides.

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Scheme 2
Synthetic strategies for the synthesis of alknyl chalcogenides. (a) Typical synthesis of alkynyl chalcogenides from terminal alkynes; (b) photoinduced synthesis of alkynyl sulfides from 1-bromoalkynes and thiols; (c) photoinduced synthesis of alkynyl sulfides from 1-bromoalkynes and diorganoyl disulfides using directing-group strategy; (d) this work: photoinduced synthesis of alkynyl selenides from 1-bromoalkynes in ionic liquids.

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Scheme 3
Scope of the photoinduced synthesis of selenoalkynes. ^aReaction conditions: 1 (0.3 mmol), 2 (0.1 mmol), [BMIm]BF₄ (1.0 g), under blue LED (100 W) and argon atmosphere for the respective reaction times indicated. ^bIsolated yields. ^cProduct observed by GC-MS in a 90:10 (3a/4a) ratio after 98% conversion of 2a. ^dIsolated yield after 100% conversion of 2b, in a 100:0 ratio of 3b:4b determined by GC-MS of the crude reaction mixture. ^eReaction carried out with 2.7 mmol of 2b and 8.1 mmol of 1a in [BMIm]BF₄ (27.0 g). ^fReactions carried out during 48 h. ^gBlue LED (200 W).

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Scheme 4
Control experiments for the synthesis of 3a. (a) Radical trapping experiment. Reaction conditions: 1a (0.3 mmol), 2a (0.1 mmol), TEMPO (4.0 equiv.), [BMIm]BF₄ (1.0 g), under blue LED (100 W) and argon atmosphere for 24 h. (b) Reaction performed in dark. 1a (0.3 mmol), 2a (0.1 mmol), [BMIm]BF₄ (1.0 g) under argon atmosphere (reaction flask covered with aluminum foil) for 24 h.

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Scheme 5
Plausible mechanism for the photoinduced synthesis of alkynylselenides 3 in [BMIm]BF₄.

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Table 1
Optimization of the reaction conditions for the synthesis of 3a

Scheme 1 Selected synthetic applications of alkynyl chalcogenides.

Scheme 2 Synthetic strategies for the synthesis of alknyl chalcogenides. (a) Typical synthesis of alkynyl chalcogenides from terminal alkynes; (b) photoinduced synthesis of alkynyl sulfides from 1-bromoalkynes and thiols; (c) photoinduced synthesis of alkynyl sulfides from 1-bromoalkynes and diorganoyl disulfides using directing-group strategy; (d) this work: photoinduced synthesis of alkynyl selenides from 1-bromoalkynes in ionic liquids.

Scheme 3 Scope of the photoinduced synthesis of selenoalkynes. ^aReaction conditions: 1 (0.3 mmol), 2 (0.1 mmol), [BMIm]BF₄ (1.0 g), under blue LED (100 W) and argon atmosphere for the respective reaction times indicated. ^bIsolated yields. ^cProduct observed by GC-MS in a 90:10 (3a/4a) ratio after 98% conversion of 2a. ^dIsolated yield after 100% conversion of 2b, in a 100:0 ratio of 3b:4b determined by GC-MS of the crude reaction mixture. ^eReaction carried out with 2.7 mmol of 2b and 8.1 mmol of 1a in [BMIm]BF₄ (27.0 g). ^fReactions carried out during 48 h. ^gBlue LED (200 W).

Scheme 4 Control experiments for the synthesis of 3a. (a) Radical trapping experiment. Reaction conditions: 1a (0.3 mmol), 2a (0.1 mmol), TEMPO (4.0 equiv.), [BMIm]BF₄ (1.0 g), under blue LED (100 W) and argon atmosphere for 24 h. (b) Reaction performed in dark. 1a (0.3 mmol), 2a (0.1 mmol), [BMIm]BF₄ (1.0 g) under argon atmosphere (reaction flask covered with aluminum foil) for 24 h.

Scheme 5 Plausible mechanism for the photoinduced synthesis of alkynylselenides 3 in [BMIm]BF₄.

Table 1 Optimization of the reaction conditions for the synthesis of 3a


entry^a	Lamp	Solvent	time / h	Conversion of 2a^b / %	Ratio (3a:4)^c
1	blue 100 W	DCM	1	68	69:31
2	blue 50 W	DCM	1	8	100:0
3	white 100 W	DCM	1	16	56:44
4	UVA 50 W	DCM	1	0	–
5	blue 100 W	DMF	1	47	89:11
6	blue 100 W	THF	1	94	62:38
7	blue 100 W	DMF	4	72	93:07
8	blue 100 W	DMF	24	72	97:03
9	Blue 100 W	DMSO	24	78	69:31
10^d	blue 100 W	[BMIm]BF₄	24	98	90:10
11^d	blue 100 W	[BMIm]PF₆	24	98	43:57
12^e	blue 100 W	[BMIm]BF₄	24	82	81:19
13^f	blue 100 W	[BMIm]BF₄	24	60	70:30

^a
Reaction conditions: 1a (0.3 mmol), 2a (0.1 mmol), solvent (1 mL), under argon atmosphere; ^b,^cdetermined by GC-MS of the crude reaction mixture; ^dreaction conditions: 1a (0.3 mmol), 2a (0.1 mmol), solvent (1 g); ^ereaction conditions: 1a (0.3 mmol), 2a (0.1 mmol), solvent (0.5 g); ^freaction conditions: 1a (0.3 mmol), 2a (0.1 mmol), solvent (1.5 g). DCM: dichloromethane; THF: tetrahydrofuran; DMF: dimethylformamide; DMSO: dimethylsulfoxide.

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