1-Chloro-2-iodoethylene

(E)

[28540-81-0]  · C2H2ClI  · 1-Chloro-2-iodoethylene  · (MW 188.40) (Z)

[31952-74-6]

(cross-coupling reagent used as a precursor of chloroenynes, terminal, and unsymmetrical internal diynes)

Alternate Name: 1-chloro-2-iodoethene.

Physical Data: 1 (E), bp 113-114 °C; mp -41.0 °C, d 2.10 g cm-3, bp of n-propanol azeotrope 87.5-88.5 °C. (Z), bp 116-117 °C; mp -36.4 °C, d 2.21 g cm-3, bp of n-propanol azeotrope 93.6-94.0 °C.

Preparative Methods: 1-chloro-2-iodoethylene can be prepared by either chloromercuration of Acetylene2 followed by iodinolysis3 or electrophilic addition of Iodine Monochloride to acetylene (eq 1).1 The chloromercuration reaction is highly stereoselective and gives exclusively the (E) isomer, while the electrophilic addition of ICl has been reported to give a diastereomeric mixture (however, this reaction has also been reported to be stereoselective4). The (E)-alkenyl mercury intermediate can be isomerized5 to an (E)/(Z) mixture by treatment with a catalytic amount of Dibenzoyl Peroxide at 100 °C in p-xylene. Its iodinolysis gives an (E) and (Z) mixture of 1-chloro-2-iodoethylenes.

Purification: stereoisomerically pure (Z)-1-chloro-2-iodoethylene can be obtained by azeotropic fractional distillation of stereoisomeric mixtures with n-propanol. Stereoisomerically pure samples can be isomerized to give a mixture of (Z) and (E) isomers upon long exposure to sunlight and should be stored accordingly.

Handling, Storage, and Precautions: use in a fume hood.

Cross-Coupling Reactions.

1-Chloro-2-iodoethylene can readily participate in selective mono-cross-coupling reactions because of the difference in reactivity between the two carbon-halogen bonds. Cross-coupling with alkylmercurials6 is nonstereospecific because of its radical nature, and leads to a mixture of diastereomers in most cases. On the other hand, Pd-catalyzed cross-coupling7 with alkynylzincs yields stereospecifically the corresponding (E)-chloroenynes (1) in good yields (eq 2).4

It is worth noting that the (Z)- or (E)-chloroenynes, e.g. (1) or (2), can also be stereospecifically prepared by Pd/Cu-catalyzed cross-coupling of alkynes with (Z)- or (E)-1,2-Dichloroethylene (eq 3).8 On the other hand, the corresponding reaction with 1,2-dibromoethylene gives a mixture of mono- and dialkynylated products.9

The chloroenynes (1) and (2) can readily participate in further cross-coupling reactions, and this methodology has been applied to the synthesis of a variety of natural products10 and oligomeric unsaturated compounds.11 Dehydrohalogenation of the chloroenynes (1) with Sodium Amide in liquid ammonia can lead to 1-sodio-1,3-diynes which, in turn, can be further transformed into terminal and symmetrical or unsymmetrical internal diynes (eq 4).4

Related Reagents.

(E)-1-Bromo-2-phenylthioethylene; 1,2-Dichloroethylene.


1. Van de Walle, H.; Henne, A. Bull. Sci. Acad. Roy. Belg. 1925, 11, 360 (CA 1926, 20, 1050).
2. Nesmeyanov, A. N.; Freidlina, R. Kh. IZV 1945, 150 (CA 1946, 40, 3451).
3. Beletskaya, I. P.; Reutov, O. A.; Karpov, V. I. IZV 1961, 1961 (CA 1963, 58, 6670h).
4. Negishi, E.; Okukado, N.; Lovich, S. L.; Luo, F. JOC 1984, 49, 2629.
5. Nesmeyanov, A. N.; Borisov, A. E. Akad. Nauk SSSR, Inst. Org. Khim., Sintezy Org. Soedinenii, Sbornik 1952, 2, 146 (CA 1954, 48, 567d).
6. Russell, G. A.; Ngoviwatchai, P.; Tashtoush, H. I.; Pla-Dalmau, A.; Khanna, R. K. JACS 1988, 110, 3530.
7. Negishi, E. ACR 1982, 15, 340.
8. Ratovelomanana, V.; Linstrumelle, G. TL 1981, 22, 315
9. Carpita, A.; Rossi, R. TL 1986, 27, 4351.
10. (a) Guillerm, D.; Linstrumelle, G. TL 1986, 27, 5857. (b) Chemin, D.; Alami, M.; Linstrumelle, G. TL 1992, 33, 2681. (c) Avignon-Tropis, M.; Berjeaud, J. M.; Pougny, J. R.; Fréchard-Ortuno, I.; Guillerm, D.; Linstrumelle, G. JOC 1992, 57, 651.
11. Bitler, S. P.; Wudl, F. Polym. Mater. Sci. Eng. 1986, 54, 292 (CA 1986, 104, 207 704u).

Ei-ichi Negishi & Christophe Copéret

Purdue University, West Lafayette, IN, USA



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