Trifluoromethanesulfonylmethyl Methyl Sulfone

[93916-15-5]  · C3H5F3O4S2  · Trifluoromethanesulfonylmethyl Methyl Sulfone  · (MW 226.22)

(equivalent of alkene polyanion1)

Alternate Name: mesyl triflone.

Physical Data: mp 115-116 °C.

Solubility: insol cold H2O; sol HCO3-, common organic solvents.

Preparative Methods: by triflation of Dimethyl Sulfone in base (EtMgBr/THF) with trifyl fluoride (CF3SO2F)1 or by analogous sulfonylation of methyl triflone (CH3SO2CF3)2 with Methanesulfonic Anhydride.

Purification: recrystallized from H2O, dried over P2O5 in vacuo.

Handling, Storage, and Precautions: stable solid, no known toxicity.

General Discussion.

The reagent acts as an alkene polyanion equivalent (2-C=C2-) owing to successive alkylations of its di- or trianion followed by base-catalyzed cheletropic extrusion of SO2 to form the product alkene (eq 1).1

The successive alkylations, or reactions with other electrophiles, proceed with regiochemical control owing to the very different acidities of the two kinds of C-H bonds at a and a. The most acidic proton (pK 4.3 in H2O) is at a, and the dianion (2 mol n-Butyllithium/THF at -78 °C) is also fully formed at the a-carbon. Alkylation of this dianion can yield either one or two alkylations at a, the former returning the stable anion of the a-monosubstituted reagent as product; the monoanion at a is very sluggish to alkylation. Successive alkylations, with added base (BuLi) and alkylating agent, proceed cleanly in the order R1, R2, R3, R4. With stoichiometric control of added base and carbon electrophile, as many as three substitutions may be carried out in one pot without isolation. Only when the a-carbon is fully substituted does treatment with base (t-BuO- was the most effective1) afford the Ramberg-Bäcklund extrusion3 of SO2; otherwise, the presence of the stable a-anion precludes it. Although the regiochemistry of substitution is well controlled, the alkene stereochemistry of the product (eq 1) is not controllable.

The final substitution (R4) requires very active alkylating agents and elevated temperatures unless it is a cyclization. a-Alkylations which provide carbonyl activation, as with a-halo carbonyls, give rise to elimination of triflinate directly (eq 2).1

Acylation at a is facile (on a,a-dianions) and requires an extra equivalent of base for the acidic a-acyl sulfone products. Aldehydes and ketones react similarly at a to afford b-hydroxy sulfones. Spontaneous cyclization occurred (eq 3) when the allylic alcohol from acrolein was oxidized to the unsaturated ketone (eq 3) and treatment with base completed the conversion to 3-methylcyclopentenone. However, mesylation of the b-hydroxy sulfone gave the four- instead of six-membered cyclization in eq 3 by direct rather than allylic displacement. Other cyclizations are shown in eq 4, the epoxide yielding only the six-membered ring, the dibromo derivative both five- and six-membered rings.

Reaction of the stable a-monoanion with Formaldehyde quantitatively eliminates triflate ion to create a-methylene sulfones (eq 5).4 Higher aldehydes did not react with the a-anion, but bromination is facile even at low temperature.

X-ray structures of several disulfones and their anions have been discussed,5 and some related ones used in synthesis. The dimesyl analog (MeSO2CH2SO2Me) also exhibits its dianion at a and is quite parallel in reactivity toward alkylation.6 As expected, the a-monoanion is more reactive and more basic (pK = 12.5). When fully substituted at a the deprotonation of phenylsulfonyl methyl sulfones at a also initiates the Ramberg-Bäcklund rearrangement with loss of phenylsulfinate ion.7 When no a-CH is available for deprotonation, treatment with base serves to eliminate triflinate, as in eq 6, and is also used to create cyclic vinyl sulfones when the a-dialkylation is done with a,o-dihalides.8

In summary, the mesyl triflone reagent is useful for preparing 1,1-disubstituted alkenes (eq 1) (R2 = R3 = H) or cyclopentenones such as dihydrojasmone.9 However, cyclohexenones were not formed1 and, while more substituted acyclic alkenes are readily obtained, they arise as cis-trans mixtures.

1. Hendrickson, J. B.; Boudreaux, G. J.; Palumbo, P. S. JACS 1986, 108, 2358.
2. Koshar, R. J.; Mitsch, R. A. JOC 1973, 38, 3358.
3. Paquette, L. A. OR 1977, 25, 1.
4. Hendrickson, J. B.; Palumbo, P. S. TL 1985, 26, 2849.
5. Grossert, J. S.; Cameron, T. S.; Hoyle, J.; Roe, S. P.; Vincent, B. R. CJC 1987, 65, 1407.
6. Castro, A.; Spencer, T. A. JOC 1992, 57, 3496.
7. Ranasinghe, M. G.; Fuchs, P. L. JACS 1989, 111, 779. Scarpetti, D.; Fuchs, P. L. JACS 1990, 112, 8084.
8. Magar, S. S.; Fuchs, P. L. TL 1992, 33, 745.
9. Hendrickson, J. B.; Palumbo, P. S. JOC 1985, 50, 2110.

James B. Hendrickson

Brandeis University, Waltham, MA, USA

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