[13698-16-3]  · C3H5Cl2NO2  · N,N-Dichlorourethane  · (MW 157.98)

(stable but reactive pseudohalogen which adds to alkenes to give b-chlorocarbamates;1 useful for the chlorination of tertiary hydrocarbons2 and activated aromatics3)

Alternate Name: DCU.

Physical Data: bp 55-56 °C/15 mmHg; 74-76 °C/15 mmHg;6 d 1.349 g cm-3.

Solubility: insol H2O; sol benzene, acetic acid, acetonitrile.

Form Supplied in: liquid; widely available; purity of commercial material 90-98%.

Analysis of Reagent Purity: by iodometric titration for positive halogen.5,6

Purification: vacuum distillation affords the reagent with a purity of >99.5%.6

Handling, Storage, and Precautions: lachrymatory liquid; fairly stable in the dark for at least several weeks at 25 °C.6,7 Store under inert atmosphere. This reagent should be handled in a fume hood.

Addition to Alkenes to give b-Chlorocarbamates.

Simple alkenes add DCU by a radical mechanism to afford, initially, b-chloro-N-chlorocarbamates, which are hydrolyzed to b-chlorocarbamates. Terminal alkenes give the products of anti-Markovnikov addition in 50-80% yields.6,7 For example, 1-hexene provides N-(2-chloro-n-hexyl)carbamate (eq 1).6

Addition to nonterminal alkenes is complicated by competing allylic chlorination; in these cases, yields of b-chlorocarbamates are generally only 30-40% (eq 2).6 Styrene and trans-stilbene give better yields of addition products with DCU (80% and 65%, respectively).6

The b-chlorocarbamate products are useful intermediates for conversion to oxazolidones (eq 3) or aziridines (eq 4).7,8

The addition of DCU to indenes,9,10 unsaturated silanes,11 and a variety of alkenes containing electron-withdrawing groups12 has been described. A review of the addition reactions of DCU with alkenes has been published.1

Chlorination of Tertiary Hydrocarbons.

Unactivated tertiary hydrogens in some steroids can be selectively replaced with chlorine by reaction with DCU under UV irradiation. The resulting chlorides have been treated with Silver(I) Perchlorate to afford alkenes (eq 5),2 or hydrolyzed to alcohols (eq 6).13

Chlorination of Activated Aromatics.

Anisole gives 4-chloroanisole in high yield with DCU; 2,4-dichloroanisole is also formed (eq 7).3 Selective monochlorination of some isoflavones has been reported.14

Other Reactions.

Organoboranes afford alkyl chlorides with DCU;4 however, other reagents, such as Chloramine-T or Trichloramine are generally more effective. 2-Substituted indoles give chlorinated 2-indolinones with DCU.15 Nitroso derivatives are oxidized with DCU in the presence of Copper(II) Bromide to provide azoxy compounds.5 Alkyl ethers can undergo cleavage reactions with DCU, to afford b-chloro(biscarbamates).3

1. Neale, R. S. S 1971, 1.
2. Mazur, Y; Cohen, Z. AG(E) 1978, 17, 281.
3. Foglia, T. A.; Swern, D. TL 1967, 3963.
4. Jigajinni, V. B.; Paget, W. E.; Smith, K. JCR(S) 1981, 376.
5. Wrobel, J.; Nelson, V.; Sumiejski, J.; Kovacic, P. JOC 1979, 44, 2345.
6. Foglia, T. A.; Swern, D. JOC 1966, 31, 3625.
7. Foglia, T. A.; Swern, D. JOC 1968, 33, 766.
8. Foglia, T. A.; Swern, D. JOC 1967, 32, 75.
9. Crookes, B.; Seden, T. P.; Turner, R. W. CC 1968, 342.
10. Walker, B. J.; Wrobel, P. J. CC 1980, 462.
11. Lukevics, E.; Dirnens, V. V.; Goldberg, Y. S.; Liepinsh; E. E.; Gavars, M. P.; Kalvinsh, I. Ya.; Shymanska, M. V. OM 1985, 4, 1648.
12. Balon; Ya. G.; Paranyuk, P. E. ZOR 1980, 16, 556.
13. Cohen, Z.; Berman, E.; Mazur, Y. JOC 1979, 44, 3077.
14. Bass, R. J. CC 1979, 264.
15. Acheson, R. M.; Prince, R. J.; Proctor, G. JCS(P1) 1979, 595.

Howard Sard

Organix, Woburn, MA, USA

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