Phenyl Selenocyanate-Copper(II) Chloride


[2179-79-5]  · C7H5NSe  · Phenyl Selenocyanate-Copper(II) Chloride  · (MW 182.09) (CuCl2)

[7447-39-4]  · Cl2Cu  · Phenyl Selenocyanate-Copper(II) Chloride  · (MW 134.45)

(oxyselenates alkenes, dienes, and a,b-unsaturated aldehydes with regio- and stereoselectivity; forms cyclic ethers)

Physical Data: see Phenyl Selenocyanate and Copper(II) Chloride.

Form Supplied in: both components are commercially available.

Preparative Methods: the reagent is prepared as needed. PhSeCN can be made5 from phenyldiazonium salts and commercially available KSeCN or, particularly for small-scale experiments, from the available reagents PhSeCl and Me3SiCN.6,7

Handling, Storage, and Precautions: selenium reagents are highly toxic and corrosive. All reactions should be conducted in a well-ventilated fume hood.

General Discussion.

Phenyl selenocyanate in alcohols, wet THF, or acetic acid/chloroform reacts, in the presence of copper(II) or -(I) chloride, on the C=C double bond of alkenes1 and dienes2,3 and produces b-alkoxy-, b-hydroxy-, and b-acetoxyalkyl phenyl selenides and cyclic ethers in good yields. The reaction is best achieved (1-10 h) at 65 °C with stoichiometric amounts of the copper salts. Although it still proceeds at lower temperature (25 °C) and with smaller amounts of catalyst (down to 0.025 mol equiv), it becomes particularly slow. It does not occur in the absence of copper salts or when a pyridine-CuCl2 complex is used.1 It has nevertheless been reported4 that this reaction can be catalyzed by copper-loaded polymers, but the yields are lower.

This reaction has been successfully carried out on terminal, alicyclic, and cyclic a,b-disubstituted alkenes as well as on vinyl acetate, a,b-unsaturated aldehydes (eq 1), and their dimethyl acetals.1 The two latter compounds provide, on reaction in methanol, the same b-methoxy-b-dimethoxyalkyl phenyl selenide. Oxyselenation does not occur with compounds possessing electron-withdrawing groups attached to the C=C double bonds, such as methyl vinyl ketone, methyl acrylate, and acrylonitrile.1 Successful reaction of a,b-unsaturated aldehydes is probably due to the intermediate formation of the corresponding a,b-unsaturated acetal.1

The oxyselenation is regioselective, the phenylseleno group being introduced at the least substituted carbon of styrene, vinyl acetate, and 1-hexene (eq 2).1 In the last case the highest ratio of primary alkyl selenide is achieved, presumably under thermodynamic control, when the reaction is performed at higher temperature and for a longer time. The selectivity is reversed with acrolein, allowing the synthesis of a-phenylseleno-b-methoxy aldehydes (eq 1).1

The reaction is stereoselective and occurs via anti addition (eq 3) except with crotonaldehyde. The intermediate formation of a seleniiranium ion might account for the reported regio- and stereoselectivity. The lower reactivity of the unsaturated aldehydes and the possible (Z/E) isomerization prior to oxyselenation might be responsible for the lower stereocontrol.

Reaction of cis,cis-1,5-cyclooctadiene with phenyl selenocyanate-copper(II) chloride in alcohols, aq THF, or acetonitrile produces2,3 a mixture of [3.3.1] and [4.2.1] bicyclic ethers in good yields (eq 4).

The isomer ratio depends upon the solvent used; a suitable choice of solvent results in a more selective formation of each isomer (eq 4). Synthesis of the [3.3.1] ethers is best achieved in methanol; aq THF provides the other isomer. The intermediate formation of a b-hydroxyalkyl selenide, rather than the corresponding ether, proved to be responsible for the result observed in aq THF. The PhSeCN-CuCl2 monitored oxyselenation reaction has been successfully applied to other dienes such as 1,5-hexadiene, diallyl ether, and diallyl sulfide (eq 5).

Related Reagents.

Copper(II) Chloride; o-Nitrophenyl Selenocyanate; Phenyl Selenocyanate.

1. Toshimitsu, A.; Aoai, T.; Uemura, S.; Okano, M. JOC 1980, 45, 1953.
2. Uemura, S.; Toshimitsu, A.; Aoai, T.; Okano, M. CL 1979, 1359.
3. Toshimitsu, A.; Aoai, T.; Uemura, S.; Okano, M. JOC 1981, 46, 3021.
4. Menger, F. M.; Tsuno, T. JACS 1989, 111, 4903.
5. Behaghel, O.; Seibert, H. CB 1932, 65, 812.
6. Tomoda, S.; Takeuchi, Y.; Nomura, Y. CL 1981, 1069.
7. Tomoda, S.; Takeuchi, Y.; Nomura, Y. S 1985, 212.

Alain Krief

Facultés Universitaires Notre-Dame de la Paix, Namur, Belgium

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