Thiobenzophenone, Diels-Alder

Bis(trifluoromethyl)-l,2,4,5-tetrazine 314 reacts with substituted thiobenzophenones by [4-h2] cycloaddition via a Diels-Alder adduct which is not isolable. Cycloreversion, with elimination of nitrogen, then gives 6/f-l,3,4-thiadi-azines 315 in yields of 47-75% (Scheme 41) <1998EJ02861>. Similarly, the treatment of 314 with alkylthioformates yields 2,5,6-substituted-6/f-l,3,4-thiadiazines <1984AGE890>. 

Treatment of 1,2,4,5-tetrathiane 55 with DMAD in refluxing mesitylene produced the benzothiopyran 148, that is, the Diels-Alder adduct of thiobenzophenone and DMAD (Scheme 19). When the reaction was carried out in chloroform in a sealed tube at 150 °C, a 36% yield of 148 was obtained, along with 26% of dithiole 149, perhaps via a competing acid-catalyzed pathway <1997H(45)507>. 

Scheme 46 5yn-x-face-selective Diels-Alder cycloaddition of 3,4-di-fert-butylthiophene 1 -oxide with thiobenzophenone [49]... 

Though normally, Diels-Alder reactions of 3,4-di-tert-butylthiophene 1-oxide and related compounds occur exclusively at the syn-n-face, exceptions have also been observed. For example, in its reaction with thiobenzophenone, two diastereo-mers 50 and 51 were obtained. The major diastereomer 50 was isolated in 76% yield, but the minor diastereomer 51 was also produced, in 15% yield, the conformation of which was established by X-ray diffraction analysis (Scheme 46). This example reveals that the reaction takes place predominantly at the syn-jr-face to the S=0 bond, though not exclusively. The jr-face selectivity was explained in terms of the extent of conformational changes of 3,4-di-[Pg.248]

The dimer of hexafluorothioacetone (217) reacts, as shown in Scheme 8, with mercuric fluoride-potassium fluoride to give the mercuric mercaptide of perfluoropropane-2-thiol in DMF, potassium flucnide promotes the reaction of (217) with alcohols, thiols, thiophenols, and olefins to give products derived from the thioacetone monomer. Reaction with styrene gave the bis-Diels-Alder adducts (218) and (219) thietan (220) is obtained with cyclohexene. Amino-alcohols, o-aminophenol, o-aminothiophenol, and o-phenylenediamine yield 2,2-bis(trifluoromethyl)-l,3-het ocyclic derivatives, e.g. (221). 1,3-Dithietans did not react with Fe2(CO) and were discarded as possible intermediates in the ortho-metallation reactions of thiobenzophenones. The hydrolysis reactions of a 1,3-cyclodisiladithietan and its reaction with o-hydroxymercuribenzoic acid have been investigated. ... 

The applicability of thioketones in the synthesis of heterocyclic compounds has been further demonstrated. The Diels-Alder reaction of thiobenzophenone with l,3>5-cycloheptatriene gave the (2 + 4) cycloadduct (101) in 40% yield. Cycloheptatrienethione (92) yielded the (8 + 2) cycloadduct (102) quantitatively by reaction with maleic anhydride, and the bicyclic compound (103) in 65% yield by reaction with dimethyl acetylenedicarboxylate. Compound (103) was considered to be a rearrangement product of the probably primarily formed (8 + 2) cycloadduct intermediate (104). " The in situ addition of nitrile oxides to aromatic thioketones resulted in formation of 1,4,2-oxathiazoles, " whereas 1,4,2-oxathiazolidines were the products in the reactions of some alicyclic thiones with nitrones. The formation of thio-ozonides (1,2,4-trithiolans) by treatment of thioketones with amines or chloramine T was investigated recently. ... 

The heavily substituted A -dihydrothiopyran (7) results from Diels-Alder addition of thiobenzophenone and 1,1,3-trimethyl-1,3-butadiene, and related spiro-compounds have been obtained from cyclic thioketones. The equilibria between tautomers (8 R = Me, Et, etc.) and (9) have been studied under acidic conditions, form (8) is always the major component. 

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