Sulfur dioxide and 1,3-butadiene react to form a five-membered cyclic unsaturated sulfone. the 2,5-dihydrothiophene 1,1-dioxide (I). When treated with a base, I will isomerize to form the 2,3-dihydrothiophene 1,1- dioxide (II). The known procedures for the preparation of I and II have been improved.

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The 2,5-dihydrothiophene 1,1-dioxide (I) is the parent member of a large group of five-membered cyclic β-sulfones while the 2,3-dihydrothiophene 1,1-dioxide (II) is the parent member of the corresponding α-sulfones.

Structurally, I contains a carbon-carbon double bond, a sulfone group and two α-methylene groups while II only has one α-methylene group but its carbon-carbon double bond is conjugated with the sulfone group. It is of considerable interest to study the chemical reactions of these two polyfunctional molecules to gain some information concerning the influence of the functional groups upon each other. Of further interest would be to compare the reactions of I and II since differences in chemical properties are to be expected since the α-sulfones have the double bond conjugated with the sulfone group while the β-sulfones do not.

Bromine adds readily to I in aprotic media to give the 3,4-dibromotetrahydrothiophene 1,1-dioxide (V). The addition of bromine to II only occurs in a water solution to give the 2,3-dibromotetrahydrothiophene 1,1-dioxide (VII). The total lack of evidence of the addition of hydrogen halides to I or II was not expected. The electrophilic attack is hindered by the presence of the sulfone group.

Free radical reactions using N-bromosuccinimide and 1,3-dibromo-5,5-dimethylhydantoin were employed with I and II. The expected allylic substitution of bromine in I at the 2 or 5 position and in II at the 3 position was not obtained but rather addition to the double bond of I and II occurred.

The dehydrobromination reaction of 3,4-dibromo-tetrahydrothiophene 1,1-dioxide (V) has been improved to give better yields of the 3-bromo-2,3-dihydrothiophene 1,1- dioxide (XIII). A new compound, the 5-bromo-2,3-dihydrothiophene 1,1-dioxide (XVIIc), has been obtained from the dehydrobromination of the 2,3-dibromo-tetrahydrothiophene 1,1-dioxide (VII).

The 3-bromo, 3-chloro and the 3-iodo-2,3-dihydrothiophene 1,1-dioxides were prepared through a series of reactions, the letter two for the first time. The 3-iodo-2,3-dihydrothiophene 1,1-dioxide (XIX) was prepared by treating the 3-bromo-2,3-dihydrothiophene 1,1- dioxide (XIII) with sodium iodide in acetone. The 3-chloro-2,3-dihydrothiophene 1,1-dioxide (XX) in turn was prepared by reacting the 3-iodo-2,3-dihydrothiophene 1,1-dioxide (XIX) with mercuric chloride in absolute ethanol. The infrared spectra of the above compounds were compared.

Since the alpha hydrogens are acidic in the cyclic unsaturated sulfones, a thorough study of Grignard reagents with the 2,5-dihydrothiophene 1,1-dioxide (I) was made. A compound, believed to be a sulfinic anhydride, was obtained from the action of the 2,5-dihydrothiophene 1,1-dioxide (I) on ethylmagnesium bromide. Some evidence in support of this sulfinic anhydride is offered. A mechanism for the Grignard reactions is proposed from the data obtained.

There was no evidence for condensation, alkylation or acylation reactions with the isomeric dihydrothiophene 1,1- dioxides.

On the basis of the reactions studied, a clearer picture of the resonance structure of the 2,5-dihydrothiophene 1,1-dioxide (I) is obtained.