Dedicated to Professor Dieter Seebach on the occasion of his 65th birthdayThe title compounds were prepared starting from pyrrolinone 4. Nucleophilic-displacement and ringclosure reactions yielded the dithiolopyrrole 5a, which formed salts with electrophiles (7, 8) as well as with bases. The crystal structure of 5a was determined. Oxidation of the dithioles 5a and 6a led to S(2)-oxides (10a, 11a) and the corresponding S(2)-dioxides (10b, 11b) depending on reaction conditions. The thiosulfinate 10a was converted by a ring-opening/ring-closure reaction sequence to the bicyclic sulfinamide 12. The oxidative addition reactions of [Pt(h 2 -C 2 H 4 ) (PPh 3 ) 2 ] (14) with the disulfides 5a and 13 led to the dithiolatoplatinum(II) complexes 15 and 16, respectively. Complex 16 was characterized structurally. The sulfenato-thiolato complex 17 was synthesized via reaction of 14 with the thiosulfinate 10a. The thiosulfonato Pt II complex 18 was prepared by an oxidative insertion of Pt 0 into the CÀS bond of the corresponding thiosulfonate 10b. Furthermore, complex 18 was characterized by single-crystal X-ray-diffraction studies.

Ozonations of alkoxy-and (acyloxy)-substituted alkylidene-lactams 1 and 5 or of the alkylidene-sultams 9 and 10 proceeded by regioselective cleavage of the exocyclic C=C bonds (Schemes 1 and 2). These bonds are part of an enamide system and, therefore, possess considerable polarity as shown by 13 C-NMR spectra. As a result, the partly known maleimides 3 and 6 or the sulfonimides 11 were obtained. Compounds 3 and 11 reacted with diazomethane to give the highly reactive bicyclic derivatives 8 and 12, respectively. The cinnamylidene-lactames 16a,b were converted by selective ozonolysis mainly into the formylmethylene lactames 17a,b (Scheme 3). The amino-substituted aldehyde 20 bears a structural relationship to the lactone antibiotic basidalin 21a. The tendency of some donor-substituted maleimides to undergo [2 + 2] cycloadditions was assessed (Scheme 4). The configuration of the photodimers 22a,b and 24a,b was established by X-ray crystallography.Introduction. -The cleavage of alkene C=C bonds by ozone to give aldehydes, ketones, and carboxylic acids was introduced into organic chemistry at the beginning of the 20 th century by Harries [1]. Ozonolyses take place under extremely mild reaction conditions and often with excellent yields. The individual course of an ozonization, however, is strongly dependent on the constitution of the starting material, the solvent, and the choice of reductive or oxidative workup conditions (for a comprehensive review, see [2]).A basic three-step mechanism was formulated by Criegee and is now bearing his name [3]. In a sequence of concerted 1,3-dipolar cycloaddition and cycloreversion, carbonyl oxides [4] are formed which are captured by internally generated carbonyl compounds in another 1,3-dipolar cycloaddition to yield ozonides. As a result, for unsymmetrical alkenes, substituent rules for the regioselective OÀO splitting in the cycloreversion step have been formulated [5] [6]. There are, however, exceptions from these rules, and the ozonide-forming step may be bypassed due to low dipolarophilicity of the carbonyl intermediate. Both is examplified in the ozonolysis of ketene acetals [7]. Modifications of the original Criegee mechanism have been introduced later [8]. An alternative mechanistic concept of ozonations was recently brought up for discussion [9]. According to the donor-acceptor concept, ozonations are regarded as oxidation reactions with radical-ion intermediates.It is well known that the C=C bond of enol ethers is readily cleaved by ozone forming a carbonyl compound and a carboxylic acid ester [10 -14]. Analogously, in the ozonolysis of enol esters, beside a carbonyl compound, a mixed carboxylic acid anhydride is

Dedicated to Professor Rolf Huisgen on the occasion of his 85th birthdayThe 1,2-dithiolosultam derivative 14 was obtained from the (a-bromoalkylidene)propenesultam derivative 9 (Scheme 1). Regioselective cleavage of the two ester groups ( 3 1b or 2b) allowed the preparation of derivatives with different substituents at C(3) in the dithiole ring (see 27 and 28) as well as at C(6) in the isothiazole ring (see 17 ± 21; Scheme 2). Curtius rearrangement of the 6-carbonyl azide 21 in Ac 2 O afforded the 6-acetamide 22, and saponification and decarboxylation of the latter yielded sulfothiolutin (30). Hydride reductions of two of the bicyclic sultams resulted in ring opening of the sultam ring and loss of the sulfonyl group. Thus the reduction of the dithiolosultam derivative 14 yielded the alkylidenethiotetronic acid derivative 33 (tetronic acid furan-2,4(3H,4H)-dione), and the lactam-sultam derivative 10 gave the alkylidenetetramic acid derivative 35 (tetramic acid 1,5-dihydro-4-hydroxy-2H-pyrrol-2-one) (Scheme 3). Some of the new compounds (14, 22, 26, and 30) exhibited antimycobacterial activity. The oxidative addition of 1 equiv. of [Pt(h 2 -C 2 H 4 )L 2 ] (36a, L PPh 3 ; 36b, L 1/2 dppf; 36c, L 1/2 (R,R)-diop) into the SÀS bond of 14 led to the cis-(dithiolato)platinum(II) complexes 37a ± c. (dppf 1,1'-bis(diphenylphosphino)ferrocene; (R,R)-diop {[(4R,5R)-2,2-demithyl-1,3-dioxolane-4,5-diyl]bis(methylene)}bis[diphenylphosphine]).

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The 4‐hydroxypyridones 7 and 3‐hydroxypyridones 8/9 (azagrevellins) were prepared by reaction of the pyrrolidinetrione 4 and diazoalkanes. The ring enlargement proceeded by anionotropic [1,2]‐rearrangement introducing carbon between C‐3 and C‐4 or, to a lesser extent, between C‐2 and C‐3 due to the different migration aptitudes of the two acyl groups involved. In a cognate manner ring expansion between C‐2 and C‐3 occured by the interaction of diazomethane and the pyrrolidinetrione hydrazone 15, to give the spiroe‐poxide 16 as the final product. From the reaction of trione 4 and diazomethane, however, the diepoxide 14 was obtained. In this case ring homologation must have taken place by insertion of carbon between C‐4 and C‐5. In a two step ring expansion the pyridones 21 and 22 were obtained from the maleineimides 17.