Bromomethanesulfonyl Bromide

[54730-18-6]  · CH2Br2O2S  · Bromomethanesulfonyl Bromide  · (MW 237.89)

(converts alkenes into 1,3-dienes1-7 including 1-vinyl-1-cycloalkenes,1,3 3-methylene-1-cycloalkenes,1,3 2-alkyl-1,3-butadienes;1,6 also converts silyl enol ethers into a-methylene ketones1,5 and alkynes into enynes1)

Physical Data: bp 68 °C/0.55 mmHg;2 n20D 1.5706.1

Solubility: sol CH2Cl2, Et2O; insol H2O.

Analysis of Reagent Purity: 1H NMR (60 MHz) d 5.05 (s, 2H).

Preparative Methods: to a stirred suspension of sym-trithiane (0.73 mol) in water was added Br2 (7.1 mol) dropwise to maintain a reaction temperature of 35-40 °C. Cooling by ice bath may be required. After the addition of Br2 is complete, the reaction is stirred for an additional 15 min. The product is extracted into CH2Cl2, washed with 5% sodium bisulfite solution, and dried. Concentration and distillation yields bromomethanesulfonyl bromide in 42-48% yield as a pale yellow liquid.1,2

Handling, Storage, and Precautions: reactive sulfonylating agent: avoid contact with skin and mucous membranes. Stable at 25 °C for at least 2 weeks. Decomposes forming CH2Br2 and SO2. Use in a fume hood.

Addition to Alkenes.

Light-initiated bromosulfonylation of alkenes occurs readily at -20 °C via a radical chain reaction and is generally more efficient than the thermal reaction (see also Benzenesulfonyl Bromide). Regioselective addition of sulfonyl bromides with mono-, 1,1-disubstituted, and 1,1,2-trisubstituted alkenes occurs to give the more substituted alkyl bromide.1,3 Chemoselective addition to alkenes is observed with nonconjugated dienes: monoalkyl > 1,1-dialkyl > 1,1,2-trialkyl. Subsequent treatment of the adducts with base yields a,b-unsaturated sulfones (eq 1). Stereoselectivity with terminal alkenes is observed, favoring the (E) configuration.1,3

a,b-Unsaturated bromomethyl sulfones are converted into 1,3-dienes upon further treatment with base via a vinylogous Ramberg-Bäcklund reaction.1-7 Employing this procedure, a variety of 1,3-diene products have been prepared (Table 1).

The g-deprotonation of a,b-unsaturated sulfones may occur syn or anti to the sulfonyl group, which would give a mixture of dienes from unsymmetrical precursors. The regioselectivity observed appears to be controlled by steric factors (Potassium t-Butoxide deprotonates at the less hindered position) and by coordination of the alkali cations to the sulfonyl group (Lithium t-Butoxide favors deprotonation syn to the sulfonyl group even when sterically hindered).

By this procedure, allylsilanes1,4 and 2-propenyl boronates7 are transformed into 1-trialkylsilyl-1,3-butadiene and electron-deficient 1,3-butadienyl-2-boronic esters, respectively (Table 1). However, reaction of allylstannanes with bromomethylsulfonyl bromide does not give the adduct but yields only allyl bromomethyl sulfone and stannyl bromides.1,4

Trimethylsilyl enol ethers are transformed into a-keto bromomethyl sulfones by bromomethylsulfonyl bromide in good yield. Subsequent treatment with 1,5-Diazabicyclo[4.3.0]non-5-ene yields a mixture of a-methylene ketones and 1,3-oxathiole 3,3-dioxide heterocycles, depending on the solvent and reaction conditions.1,5 Good yields of a-methylenecycloheptanone can be obtained (eq 2).

1. Block, E.; Aslam, M.; Eswarakrishnan, V.; Gebreyes, K.; Hutchinson, J.; Iyer, R.; Laffitte, J.-H.; Wall, A. JACS 1986, 108, 4568.
2. Block, E.; Aslam, M. OS 1987, 65, 90.
3. Block, E.; Aslam, M. JACS 1983, 105, 6164.
4. Block, E.; Aslam, M.; Eswarakrishnan, V.; Wall, A. JACS 1983, 105, 6165.
5. Block, E.; Aslam, M.; Iyer, R.; Hutchinson, J. JOC 1984, 49, 3664.
6. Block, E.; Eswarakrishnan, V.; Gebreyes, K. TL 1984, 25, 5469.
7. Guennouni, N.; Rasset-Deloge, R.; Carboni, B.; Vaultier, M. SL 1992, 7, 581.

John L. Esker & Carl R. Johnson

Wayne State University, Detroit, MI, USA

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