Reactions of 4-Thiazolidinones

Conversion of the 4-C=0 group of 62 into a thione function creates an isomer of rhodanine (5) called isorhodanine (87 R = H), which displays enhanced chemical reactivity. Treatment of 62 with phosphorus pentasulfide in dioxane affords 87.114-117 Isorhodanines (87) react with 

Activated ketones, for example isatin136 or acenaphthenequinone,137 have been similarly condensed with 92 at ca. 150° for several hours with acetic acid and sodium acetate forming, for example, 94, 3, or 42. Fusing 87 (R = Ph) with excess phthalic anhydride in the presence of an alkaline catalyst gives (84%) spiro[2-oxo-3-phenyl-4-thioxo-l,3-thiazolidine-5,2 -indane-1, 3 -dione] (95).117 

The 5-arylidene derivatives (e.g.,96) react with Grignard reagents via 1,4-conjugate addition to the exocyclic double bond to afford 97 [Eq. (28)] heterocyclic ring opening does not occur under these conditions.121 126,134,138 Other nucleophiles, such as p-thiocresol and piperidine, add 1,4 to exocyclic double bonds to give the simple adducts 97 (R = SAr and NR 2, respectively). 134 5-Methyl-3-phenyl-2-phenylimino-4-thiazolidinone undergoes 

Catalytic reduction of the 5-exocyclic bond cannot easily be accomplished due to the presence of the sulfur however, sodium amalgam reduces the bond in good yields.128 Bromination of the exocyclic bond is reported.20,22,24 

Treatment of 2,3-diphenyl-5-benzylidene-4-thiazolidinone with aluminum chloride (3.5 mol) in benzene results (perhaps unexpectedly) in the formation (70%) of 2,3,5-triphenyl-5-benzyl-4-thiazolidinone, by 1,2-addition to the exocyclic bond.139 

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The intramolecular cyclization reaction of 4-thiazolidinones 290, promoted by iodine in the presence of potassium iodide (or by reaction with methyl iodide in methanol), gives thiazolo[4,3-A [l,3,4]oxadiazoles 110 and 341 (Equation 63) (Table 54) <2001IJC(B)440, 1996JCR(S)388>. 

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