Sulfones cycloadditions

One approach is to use the native oxygen groups as a reagent and site of attachment. Usually, only one kind of group can be used for the reaction. As a result, only part of the surface is available for reaction, even when oxidized blacks are used. Another approach is to use the most abimdant part of the surface, carbon, for the reaction. Several methods of this type have been explored including those based on diazonium chemistry, azo chemistry, peroxide chemistry, sulfonation, cycloaddition chemistry and other methods. ... 

Cycloaddition of allyl cations to conjugated dienes provides a route to seven-membered carbocycles. One of several methods can be used to generate the allyl cation, such as from an allyl halide and silver trifluoroacetate, or from an allyl alcohol by way of its trifluoroacetate or sulfonate. Cycloaddition of the allyl cation proceeds best with a cyclic diene, particularly for intermolecular reactions. Thus, cyclohexadiene and methylallyl cation gave the bicyclo[3.2.2]nonadiene 187 (3.125). Many intramolecular examples are known, such as the formation of the... 

Benzo[6]thiophene, methoxynitro-Meisenheimer complexes, 4, 816 Benzo[6]thiophene, 2-methyl-cycloaddition reactions, 4, 793 protonation, 4, 47 sulfonation, 4, 764 synthesis, 4, 879, 915 Benzo[6]thiophene, 3-methyl-cycloaddition reactions, 4, 793 1-oxide... 

Diels-Alder cycloaddition reactions, 2, 350 tautomerism, 2, 27, 152, 347 Isoquinoline, 4-hydroxy-alkylation, 2, 349 sulfonation, 2, 321... 

The following compounds have been obtained from thiete 1,1-dioxide Substituted cycloheptatrienes, benzyl o-toluenethiosulfinate, pyrazoles, - naphthothiete 1,1-dioxides, and 3-subst1tuted thietane 1,1-dioxides.It is a dienophile in Diels-Alder reactions and undergoes cycloadditions with enamines, dienamines, and ynamines. Thiete 1,1-dioxide is a source of the novel intermediate, vinylsulfene (CH2=CHCH=SQ2). which undergoes cyclo-additions to strained olefinic double bonds, reacts with phenol to give allyl sulfonate derivatives or cyclizes unimolecularly to give an unsaturated sultene. - Platinum and iron complexes of thiete 1,1-dioxide have been reported. 

Alkynyl trifluoromethyl sulfones add dimethylformamide and dimethylsul-foxide to give products in good yields The consistent stereospeciticity of the reaction syn addition product only) suggests that an unstable [2+2] cycloaddition intermediate is initially formed [J4] (equation 12). 

Similar cycloaddition reactions were observed with methyl vinyl sulfone (48) and )3-nitrostyrene (48,51). Methyl vinyl ketone, on the other hand, is reported to give dihydropyrans as the initial products (50,52,53). Thus (16) on reaction with methyl vinyl ketone at room temperature for 12 hr gave a 60% yield of 2-dimethylamino-3,3,6-trimethyl-3,4-dihydro-2H-pyran (59). 

Methyl vinyl sulfone forms 1,2-cycloaddition adducts with aldehydic enamines, both with and without 3 hydrogens (37). Simple alkylation was reported to take place when phenyl vinyl sulfone was allowed to react with cyclohexanone enamines (58,60), but it has recently been shown that phenyl vinyl sulfone also forms cyclobutane adducts (60a). 

Enaminoketones undergo 1,4 cycloadditions with sulfene (162a). This is illustrated by the reaction of enamine 120 with sulfene to form sulfone 121 in an 80 % yield (162,163). 

As formal a, /i-unsaturated sulfones and sulfoxides, respectively, both thiirene dioxides (19) and thiirene oxides (18) should be capable, in principle, of undergoing cycloaddition reactions with either electron-rich olefins or serving as electrophilic dipolarophiles in 2 + 3 cycloadditions. The ultimate products in such cycloadditions are expected to be a consequence of rearrangements of the initially formed cycloadducts, and/or loss of sulfur dioxide (or sulfur monoxide) following the cycloaddition step, depending on the particular reaction conditions. The relative ease of the cycloaddition should provide some indication concerning the extent of the aromaticity in these systems2. 

The cycloaddition of thiirene dioxide with phenyldiazomethane gave 3,4,5-triphenylpyrazole (165a) and the acyclic a-diazobenzyl 1,2-diphenylvinyl sulfone (164a), both suggested to originate in the common 1,3-dipolar cycloaddition intermediate 1626 (equation 66). Diphenylthiirene dioxide reacts similarly with other diazoalkanes (161b-e). 

It appears, however, that the most used strategy for the preparation of thietane dioxides is the [2 + 2] cycloaddition of enamines (202) with in situ-generated sulfenes (220)74,143,186 188,202,242 to give /(-aminothietane sulfones (equation 85). 

Practically speaking, almost all syntheses of these systems are based on the enamine-sulfene cycloaddition reaction143 250. The thietane sulfone thus obtained yields, by elimination of R2NH, the desired unsaturated, four-membered sulfone system187 189 231 250 251 (equation 87). 

Based on the high dienophilicity of acyclic vinyl sulfones one should expect thiete dioxides to exhibit similar properties. Indeed, several Diels-Alder (2 +4) cycloadditions with thiete dioxide as dienophile are known. For example, 1,3-butadiene and 1,3-diphenylisobenzofuran react with 3-chloro- or 3-bromo-thiete dioxides to afford the corresponding 1 1 Diels-Alder cycloadducts255 277 (equation 105). 

Cycloadditions of the 1,3-dipolar nitrile oxides and diazoalkenes to acyclic vinyl sulfones are in general highly selective, the particular regioisomer formed depending on the substituents of both reactants213,214. Nitrones, on the other hand, tend to yield mixtures of the two possible isomers (see equation 78). 

Since sulfoxides and sulfones are versatile synthetic intermediates, and since in both the thiolene oxide and dioxides the reverse dethionylation114 ( — SO), and cheletropic extrusion of sulfur dioxide296, respectively, readily take place thermally, these cycloadditions are expected to find a useful place in organic synthesis. It should be kept in mind, however, that the retrograde SO-diene reaction and interconversion of the thiolene oxides compete effectively against SO extrusion on heating, and that diene isomerization accompanies the forward reaction (SO + diene). 

Since the first demonstration of a cycloaddition reaction of a, /f-unsaturated sulfones in 1938 by Alder and coworkers85, a variety of a, /3-unsaturated sulfones have been prepared and used as dienophiles. For example, when a mixture of p-tolyl vinyl sulfone and 2,3-dimethylbutadiene in benzene is heated at 145-150 °C for 10 h in a sealed tube, crystals of the cycloadduct (134) are obtained (equation 102). Other examples of this intermolecular cycloaddition reaction are given in Table 12. 

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