Dichloroborane-Dimethyl Sulfide1

BHCl2.SMe2

[63462-42-0]  · C2H7BCl2S  · Dichloroborane-Dimethyl Sulfide  · (MW 144.85)

(hydroborating agent suitable for the hydroboration of labile alkenic structures;2 provides access to alkyldichloroboranes and alkenyldichloroboranes3,4)

Alternate Name: DCBS.

Physical Data: d420 = 1.255 g cm-3.

Solubility: sol benzene, carbon tetrachloride, dichloromethane, diethyl ether, THF.

Form Supplied in: colorless to pale yellow liquid.

Analysis of Reagent Purity: hydrolyze an aliquot and measure the hydrogen evolved according to the standard procedure.7a 11B NMR (CCl4): d, ppm, 2.0;7b 1.7 (d);7c 2.2 (d, JB-H = 157.42 Hz).5

Preparative Methods: by redistribution of Borane-Dimethyl Sulfide (BMS) and BCl3.SMe2.5 A mixture containing BHCl2.SMe2 (73%) and BMS, BH2Cl.SMe2, and BCl3.SMe2 is obtained by the reaction of BMS with Ph3CCl.6

Handling, Storage, and Precautions: corrosive, air- and moisture-sensitive, flammable liquid; stench. Reacts violently with water. Handle and store under nitrogen or argon. Stable indefinitely when stored under nitrogen at 25 °C. Destructive to upper respiratory tract, eyes, and skin. Handle in a fume hood.

Hydroboration of Alkenes and Alkynes.

The hydroboration of alkenes with dichloroborane-dimethyl sulfide (DCBS) in refluxing dichloromethane produces considerable quantities of R2BCl and R3B as impurities, presumably as the result of disproportionation of the reagent. The addition of boron trichloride liberates dichloroborane and the hydroboration proceeds cleanly at 25 °C (eq 1)3 (see Dibromoborane-Dimethyl Sulfide for direct hydroboration of alkenes).

DCBS is highly regioselective,8 exhibiting the directive effects similar to those observed for Monochloroborane Diethyl Etherate.9 Alkyldichloroboranes are readily isolated by distillation under vacuum. Methanolysis provides the corresponding alkylboronic esters (eq 2).3 Alkenylboronic esters can be obtained from alkynes (eq 3).4

A characteristic feature of alkyldichloroboranes is their exceptional resistance to thermal isomerization, making possible the regio- and stereoselective synthesis of organoborane intermediates from highly labile alkenic structures. Thus the organoborane intermediate initially formed in the hydroboration of 1-methylcyclooctene with Borane-Tetrahydrofuran undergoes facile isomerization, even at 0 °C, to a mixture of regio- and stereoisomeric organoboranes (eq 4).10 In contrast, the hydroboration of 1-methylcyclooctene with DCBS at 0 °C affords cleanly trans-(2-methylcyclooctyl)dichloroborane in excellent yield and purity (eq 5).2

An intramolecular version of the reaction of alkyldichloroboranes with organic azides has been employed in a highly stereoselective synthesis of trans-cycloalkanopiperidines and cycloalkanopyrrolidines (eq 6)11 (for the synthesis of other secondary amines, see Dibromoborane-Dimethyl Sulfide and Dichloroborane Diethyl Etherate).

Alkyldichloroboranes can be converted into a host of valuable organoborane intermediates via the hydridation-stepwise hydroboration procedure.12 The procedure enables a general synthesis of unsymmetrical dialkylboranes and totally mixed trialkylborane intermediates for the synthesis of ketones and tertiary alcohols, respectively.12b

Transmetalation.

The reagent has been used in the synthesis of bis(2,4,6-triisopropylphenyl)borane ((trip)2BH) by the transmetalation reaction (eq 7).13 (Trip)2BH belongs to the family of highly hindered borane reagents like dimesitylborane.14 It is a rare example of a monomeric disubstituted borane.13


1. (a) Brown, H. C.; Zaidlewicz, M. Polish J. Appl. Chem. 1982, 26, 155. (b) Brown, H. C.; Kulkarni, S. U. JOM 1982, 239, 23. (c) Pelter, A.; Smith, K. COS 1991, 8, 703.
2. Brown, H. C.; Racherla, U. S. JOC 1983, 48, 1389.
3. Brown, H. C.; Ravindran, N.; Kulkarni, S. U. JOC 1980, 45, 384.
4. Brown, H. C.; Bhat, N. G. JOC 1988, 53, 6009.
5. Brown, H. C.; Ravindran, N. IC 1977, 16, 2938.
6. Bolton, R.; Gates, P. N.; Jones, S. A. W. AJC 1987, 40, 987.
7. (a) Brown, H. C. Organic Synthesis via Boranes, Wiley: New York, 1975; p 239. (b) Paget, W. E.; Smith, K. CC 1980, 1169. (c) Shiner, C. S.; Garner, C. M.; Haltiwanger, R. C. JACS 1985, 107, 7167.
8. Brown, H. C.; Racherla, U. S. JOC 1986, 51, 895.
9. Brown, H. C.; Ravindran, N. JACS 1976, 98, 1785.
10. (a) Brown, H. C.; Zweifel, G. JACS 1961, 83, 2544. (b) Brown, H. C.; Klimisch, R. L. JACS 1966, 88, 1430.
11. Brown, H. C.; Salunkhe, A. M. TL 1993, 34, 1265.
12. (a) Brown, H. C.; Kulkarni, S. U. JOM 1981, 218, 299. (b) Kulkarni, S. U.; Basavaiah, D.; Zaidlewicz, M.; Brown, H. C. OM 1982, 1, 212.
13. Bartlett, R. A.; Diaz, H. V. R.; Olmstead, M. M.; Power, P. P.; Weese, K. J.; Tirpz, H. B. OM 1990, 9, 146.
14. Pelter, A.; Smith, K.; Brown, H. C. Borane Reagents, Academic: London, 1988; pp 189 and 336.

Marek Zaidlewicz

Nicolaus Copernicus University, Torun, Poland

Herbert C. Brown

Purdue University, West Lafayette, IN, USA



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