Sulfines dimerization reactions

Pentafluorophenyl thioketones are available [115] from the reaction of the corresponding fluoroketones with B2S3 formed in situ. Oxidation with monoperphthalic acid generated the sulfine, the X-ray structure of which revealed a dimer in the crystal lattice. 

The addition sequence may determine the primary reaction course or influence impurity formation. For example, condensation of diethyl 3-oxoglutarate 33 with chloroacetone and methylamine is expected to give the 5-methylpyrrole 34, the Hantzch pyrrole product (Figure 5.14). The isomeric 4-methylpyrrole 35 (a precursor to zomepirac sodium) was prepared in good yield by first treating 33 with methylamine, then adding chloroacetone [22]. The addition sequence was also important for the chlorination of the sulfinate anion 36 The dimer 37 was produced when N-chlorosuccinimide was added to the reaction, but when 36 was added slowly to excess Cl2, the desired sulfonyl chloride 38 was produced (Figure 5.14) [23], The course of these reactions may be predicted if one takes a mental snapshot of them. 

When 2-alkylsulfinyl-, 2-arylsulfinyl-, and 1,2-aralkylsulfinyl-benzimidazoles react with thiols, the unsymmetrical disulfides are obtained (instead of the symmetrical ones), together with ipso-substitution products. The reaction is believed to be initiated by protonation of the benzimidazole nitrogen. The sulfenic acid is then eliminated after the ipso-substitution by thiolate. The sulfonic acid, once formed, is so unstable that it reacts immediately with thiol or dimerizes to form thio-sulfinates from which the unsymmetrical disulfides are derived (Equation (56)) <87JOC4620>. 

The in situ generation of the <, /3-unsaturated sulfine 24 via thermolytic retro Diels-Alder reaction of its dimer and subsequent reactions with the representative dienophiles, acrylonitrile and styrene, provided a regioiso-meric mixture of Diels-Alder products in modest yields [Eq. (19)]. 

Numerous heterocyclic compounds can be oxidized with ozone to deliver derivatives useful in synthesis and the reaction products can be tuned according to the additives and conditions in the reaction medium. When treated with ozone, pyrimidine-2-thiones and 2-thiouracils react to give several p3Timidine derivatives (eq 57). Use of aprotic solvents or ozonolysis without an active nucleophile yields dimerization products, whereas ozonolysis in protic solvents or in the presence of a nucleophile leads to the sulfinic acid derivative that can then be converted to several products depending on workup conditions. The parent pyrimidine can be isolated when acid is introduced into the medium, and with an equal volume of water the pyrimidinone product is isolated. While a protic solvent, EtOH in the medium acts as a nucleophile to deliver the 2-ethoxypyrimidine. 

In contrast to the sulfenes, the [2-1-2] cycloaddition reactions of sulfines are not well known. The dimerization of ethylsulfine gives rise to a four-membered ring rra 5-3,4-diethyl-l,2-dithietane 1,1-dioxide, which is not the result of a [2-1-2] cycloaddition Similarly, reaction... 

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