Cycloadditions 1.6- dienes, tetrachlorothiophene dioxide

A detailed discussion of the earlier work on this can be found in CHEC-I. The cycloaddition of tetrachlorothiophene-1,1-dioxide with azulene takes place in the [4 + 2]mode rather than a [4 + 6]mode. A frontier orbital-based explanation has been provided for this <85TL2607). 2-Menthyl-3,4,5-trihalothiophene-1,1-dioxides have been found to be asymmetric diene equivalents <88T3I27>. Dienophiles such as styrene, allyl alcohol and acrylamide lead to regio- and stereoisomerically pure adducts, which then eliminate SO2 to form dihydrobenzene derivatives. 

Cycloaddition with Alkenes. Tetrachlorothiophene dioxide (TCTD) undergoes a [4 + 2]cycloaddition with olefins to give an unstable 7-thiabicyclo[2.2.1]heptene dioxide which rapidly extrudes SO2 in a cheletropic reaction yielding a 1,2,3,4-tetrachloro-cyclohexa-1,3-diene (eq 1). The primary product has never been observed but it seems plausible as with 3,4-dichlorothiophene dioxide the analogous 7-thiabicyclo[2.2.1]heptene dioxide can be obtained. The broad scope of this reaction is given in the pioneering paper of Raasch. ... 

The Diels-Alder reaction between tetrachlorothiophene dioxide and maleimide yields a symmetrical product. If the diene and dienophile are asymmetrically substituted, several diastereomeric products can be formed. In principle, antibody catalysts could be prepared for each of the possible stereochemical pathways by synthesizing the corresponding transition state analogs. The preparation of antibodies that steer a Diels-Alder cycloaddition down a normally disfavored exo pathway demonstrates the feasibility of this proposition [41]. The substituted bicyclo[2.2.2]octane derivative 20, corresponding to the transition state for exo addition of acrylamide to diene 18, served as a template for generating antibodies that catalyze formation of the exo adduct 19 [41]. Catalysts for the endo pathway were prepared with the epimer of hapten 20. In both cases, a single enantiomer of the cyclohexene product was produced. 

Raasch showed that 3,4-dichloro-, tetrabromo-, and tetrachlorothiophene 1,1-dioxides react with a range of cyclic and acyclic non-conjugated dienes to give polycyclic compounds in good yields by [4+2] cycloaddition followed by intramolecular [4+2] cycloaddition [35]. For example, the Diels-Alder reaction of these dioxides with 1,5-cyclooctadiene produces the adducts 80, which then undergo an intramolecular Diels-Alder reaction to give polycyclic compounds 81 in good yields in one pot (Scheme 47). In this way, a variety of polycyclic compounds, shown below, were synthesized (Table 10). 

Scheme 97 [4+2] intermolecular Diels-Alder cycloaddition followed by intramolecular [4+2] cycloaddition of 3,4-dichloro-, tetrabromo-, and tetrachlorothiophene 1,1 -dioxides with cyclic and acyclic non-conjugated dienes [103]... 

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