Sulfones unsaturated, cycloaddition

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. 

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. 

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). 

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. 

Recent synthetic applications of the photochemical [2 + 2] cycloaddition of unsaturated sulfones have been noted. Musser and Fuchs84 have effected an intramolecular [2 + 2] addition of a 6-membered ring vinyl sulfone and a five-membered ring vinylogous ester in excellent yield, as part of a synthetic approach to the synthesis of the mould metabolite, cytochalasin C. The stereospecificity of the addition was only moderate, however, and later problems with this synthetic approach led to its abandonment. Williams and coworkers85 have used the facile [2 + 2] photoaddition of 73 and... 

However, most asymmetric 1,3-dipolar cycloaddition reactions of nitrile oxides with alkenes are carried out without Lewis acids as catalysts using either chiral alkenes or chiral auxiliary compounds (with achiral alkenes). Diverse chiral alkenes are in use, such as camphor-derived chiral N-acryloylhydrazide (195), C2-symmetric l,3-diacryloyl-2,2-dimethyl-4,5-diphenylimidazolidine, chiral 3-acryloyl-2,2-dimethyl-4-phenyloxazolidine (196, 197), sugar-based ethenyl ethers (198), acrylic esters (199, 200), C-bonded vinyl-substituted sugar (201), chirally modified vinylboronic ester derived from D-( + )-mannitol (202), (l/ )-menthyl vinyl ether (203), chiral derivatives of vinylacetic acid (204), ( )-l-ethoxy-3-fluoroalkyl-3-hydroxy-4-(4-methylphenylsulfinyl)but-1 -enes (205), enantiopure Y-oxygenated-a,P-unsaturated phenyl sulfones (206), chiral (a-oxyallyl)silanes (207), and (S )-but-3-ene-1,2-diol derivatives (208). As a chiral auxiliary, diisopropyl (i ,i )-tartrate (209, 210) has been very popular. 

Some additional examples, where the stereochemical outcome of the cycloaddition to chiral alkenes has been explained in terms of the Houk-Jager model, should also be mentioned. The diastereomer ratio found in the reaction of y-oxy-a,p-unsaturated sulfones (166), with Morita-Baylis-Hillman adducts [i.e., a-(a -hydro-xyalkyl)-acrylates (167)] (Scheme 6.27), with dispiroketal-protected 3-butene-1,2-diol (168), and with a,P-unsaturated carbonyl sugar and sugar nitroolefin (169) derivatives, all agree well with this model. 

Chiral crotonates derived from S-citroncllol, l-(—)-menthol, and S-solketol undergo 1,3-dipolar cycloaddition with cyclic and acyclic nitrones.66 Asymmetric 1,3-dipolar cycloaddition of optically active hifluoromethylated a, /l-unsaturated aiyl sulfones (43) with nitrones yield the corresponding isoxazolidmes (44) and (45) with high regio- and... 

Carretero et al. reported that enantiopure y-oxygenated-a.P-unsaturated sulfone (143) underwent a completely regioselective 1,3-dipolar cycloaddition with ace-... 

Asymmetric cycloadditions of TMM-Pd complexes of type III have been achieved based essentially on the use of chiral olefins, including vinylsul-foxides [43], y-alkoxy-o, -unsaturated sulfones [44], sugar-derived acrylates [45], lactones [46], and lactams [47]. For instance, chiral naphtoxy-... 

Aryl vinyl sulfones (17) undergo electrocatalytic cycloaddition to tra 5-l,2-diarylsulfonyl-cyclobutane (20-75%) in dry DMF (Et4NC104) (Scheme 2), when electrolysis (0.1-0.2 F) is carried out at a potential corresponding to the foot of the reduction peak or by application of an electron transfer mediator [85]. In DMSO (LiC104), up to 95% of the cyclobutane could be obtained after passage of 0.1 F [86]. No cyclobutane was formed in MeCN [86]. When reduction of 17a was carried out at the reduction peak potential in the presence of a small excess of PhOH or AcOH, a 2 1 mixture of the hydrogenation product and an unsaturated dimer was obtained [Eq. (5)] in an overall 1-F process [87]. The reaction pathway is not known. 

Unsaturated sulfones in which the sulfone moiety is directly attached to the alkenyl or alkynyl group undergo a range of cycloaddition reactions, including [2 + 2], [3 + 2] and [4 + 2] processes. 

As a typical cyclic a,/ -unsaturated sulfone, benzo[ ]thiophene 1,1-dioxide 38 participates in [2+4] cycloadditions (Scheme 31) [135]. 

---