Bildung von 1,2,4-Trithiolanen in Dreikomponenten-Gemischen aus Phenyl-azid,aromatischen Thioketonen und 2,2,4,4-Tetramethylcyclobutanthionen: Eine Schwefel-Transfer-Reaktion unter Bildung von ‘Thiocarbonylthiolaten’ ((Alkylidensulfonio)thiolaten) als reaktive Zwischenstufen

Formation of 1,2,4-Trithiolanes in Three-Component Reactions of Phenyl Azide, Aromatic Thiones, and 2,2,4,4-Tetramethylcyclobutanethiones: A Sulfur-Transfer Reaction to ‘Thiocarbonyl-thiolates’ ((Alkylidenesulfonio)-thiolates) as Reactive Intermediates The reaction of PhN₃ and aromatic thioketones 18 (two-component reaction) at 80° yields only the corresponding imines 22 , S, and N₂. Under similar conditions, in the presence of sterically crowded 2,2,4,4-tetramethyl-cyclobutanethiones 19 (three-component reaction), 1,2,4-trithiolanes of type 20 are formed in good yields in addition to imines 22 (Scheme 4). In case of 19a and 19c (X = CO, CS), the symmetrical trithiolanes 21a and 21b , respectively, are also isolated. With 4,4-dimethyl-2-phenyl-1,3-thiazole-5(4H)-thione ( 24 ) instead of aromatic thioketone 18 , imine 25 , trithiolane 21a , and 1,4,2-dithiazolidine 26 are formed (Scheme 5). A reaction mechanism for the formation of 1,2,4-trithiolanes 20 and 21 , including an S-transfer to generate ‘thiocarbonyl-thiolates’ 2b and/or 2c and 1,3-dipolar cycloaddition with a thioketone, is proposed in Scheme 7.     

Regioselektive 1,3-Dipolare Cycloadditionen eines ‘Thiocarbonyl-methanids’ ((Alkylidensulfonio)methanids) mit aromatischen Sulfinen

Regioselective 1,3-Dipolar Cycloadditions of a ‘Thiocarbonyl-methanide’ ((Alkylidenesulfonio)methanide) with Aromatic Sulfines Reaction of the spirocyclic 2,5-dihydro-1,3,4-thiadiazole 7 and thiobenzophenone S-oxide ( 6a ) in THF at 45° yielded the spirocyclic 1,3-dithiolane 1-oxide 8 , thiirane 9 , and the diazane derivative 10 in a ratio of 61:15:23 (Scheme 2). The formation of 8 is rationalized by a 1,3-dipolar cycloaddition of ‘thiocarbonyl-methanide’ 1 , generated from 7 by thermal elimination of N₂, and the C?S bond of sulfine 6a . Cyclization of intermediate 1 leads to thiirane 9 . Under the same conditions, 7 and adamantane-2-thione S-oxide ( 6b ) or 2,2,4,4-tetramethyl-3-thioxocyclobutanone S-oxide ( 4 ) reacted to give only 9 and 10 but no cycloadduct of type 8 (Scheme 4). With the aim to favor the formation of 8 , a mixture of 6a and 1.1 equiv. of 7 was heated to 45° without any solvent in a sealed tube. The ratio of products was only slightly different from that of the thermolysis in THF. An analogous experiment with 7 and 9H-fluorene-9-thione S-oxide ( 6c ) yielded cycloadduct 13 and 9 (Scheme 5). It is most interesting that the 1,3-dipolar cycloadditions of 1 and the sulfines 6a and 6c proceeded with different regioselectivity. A reaction mechanism for the unexpected formation of 10 is proposed in Scheme 7. The key step is the base-catalyzed ring opening of 7 and the nucleophilic addition of the thereby formed thiolate 21 onto the sulfonium ion 19 .     

Umsetzung von Diazoessigsäure-ethylester mit 1,3-Thiazol-5(4H)-thionen

Reaction of Ethyl Diazoacetate with 1,3-Thiazole-5(4H)-thiones Reaction of ethyl diazoacetate ( 2a ) and 1,3-thiazole-5(4H)-thiones 1a,b in Et₂O at room temperature leads to a complex mixture of the products 5–9 (Scheme 2). Without solvent, 1a and 2a react to give 10a in addition to 5a–9a . In Et₂O in the presence of aniline, reaction of 1a,b with 2a affords the ethyl 1,3,4-thiadiazole-2-carboxylate 10a and 10b , respectively, as major products. The structures of the unexpected products 6a, 7a , and 10a have been established by X-ray crystallography. Ethyl 4H-1,3-thiazine-carboxylate 8b was transformed into ethyl 7H-thieno[2,3-e][1,3]thiazine-carboxylate 11 (Scheme 3) by treatment with aqueous NaOH or during chromatography. The structure of the latter has also been established by X-ray crystallography. In the presence of thiols and alcohols, the reaction of 1a and 2a yields mainly adducts of type 12 (Scheme 4), compounds 5a,7a , and 9a being by-products (Table 1). Reaction mechanisms for the formation of the isolated products are delineated in Schemes 4–7: the primary cycloadduct 3 of the diazo compound and the C?S bond of 1 undergoes a base-catalyzed ring opening of the 1,3-thiazole-ring to give 10 . In the absence of a base, elimination of N₂ yields the thiocarbonyl ylide A ′, which is trapped by nucleophiles to give 12 . Trapping of A ′, by H₂O yields 1,3-thiazole-5(4H)-one 9 and ethyl mercaptoacetate, which is also a trapping agent for A ′, yielding the diester 7 . The formation of products 6 and 8 can be explained again via trapping of thiocarbonyl ylide A ′, either by thiirane C (Scheme 6) or by 2a (Scheme 7). The latter adduct F yields 8 via a Demjanoff-Tiffeneau-type ring expansion of a 1,3-thiazole to give the 1,3-thiazine.     

‘Three-Component Reaction’ with aromatic thioketones,phenyl azide,and dimethyl fumarate

The reaction of thiobenzophenone (= diphenylmethanethione; 8a ) or 9H-fluorene-9-thione ( 8b ) and methyl fumarate ( 9 ) in excess PhN₃ at 80° yields a mixture of diastereoisomeric thiiranes 10 and 11 (Scheme 1). A mechanism involving the initial formation of 1-phenyl-4, 5-dihydro-1H-1, 2, 3-triazole-4, 5-dicarboxylate 12 by 1, 3-dipolar cycloaddition of PhN₃ and 9 is proposed in Scheme 2. The diazo compound 13 , which is in equilibrium with 12 , undergoes a further 1, 3-dipolar cycloaddition with thioketones 8 to give 2, 5-dihydro-1, 3, 4-thiadiazoles 14 . Elimination of N₂ yields the thiocarbonyl ylide 15 which cyclizes to the corresponding thiirane. Desulfurization of the thiiranes 10 and 11 with hexamethylphosphorous triamide leads to the olefinic compounds 16 (Scheme 3). The crystal structures of 10a , 11a , and 16b were determined.     

Carbenoid Reactions of Dimethyl Diazomalonate with Aromatic Thioketones and 1,3-Thiazole-5(4H)-thiones

Dimethyl diazomalonate ( 4 ) and thiobenzophenone ( 2a ) do not react in toluene even after warming to 50°. After addition of catalytic amounts of Rh₂(OAc)₄, a smooth reaction under N₂ evolution afforded a mixture of thiiranedicarboxylate 5 and (diphenylmethylidene)malonate 6 (Scheme 2). A reaction mechanism via an intermediate ‘thiocarbonyl ylide’ 7 , formed by the addition of the carbenoid species 8 to the S-atom of 2a , is plausible. Similar reactions were carried out with 9H-xanthene-9-thione ( 2b ), 9H-thioxanthene-9-thione ( 2c , Scheme 4), and 1,3-thiazole-5(4H)-thione 18 (Scheme 6). In the cases of 2b and 2c , spirocyclic 1,3-dithiolanetetracarboxylates 14a and 14b , respectively, were obtained as the third product. Reaction mechanisms for their formation are proposed in Scheme 5: S-transfer from intermediate thiirane 12 to the carbenoid species yielded thioxomalonate 15 which underwent a 1,3-dipolar cycloaddition with ‘thiocarbonyl ylide’ 16 . An alternative is the formation of ‘thiocarbonyl ylide’ 17 via carbene addition to 15 , followed by 1,3-dipolar cycloaddition with 2b and 2c , respectively.     

1,3-Dipolare Cycloadditionen eines Carbonyl-ylids mit 1,3-Thiazol-5(4H)-thionen und Thioketonen

1,3-Dipolar Cycloadditions of a Carhonyl-ylide with 1,3-Thiazole-5(4H)-thiones and Thioketones Inp-xylene at 150°, 3-phenyloxirane-2,2-dicarbonitrile ( 4b ) and 2-phenyl-3-thia-1-azaspiro[4.4]non-1-ene-4-thione ( 1a ) gave the three 1:1 adduets trans- 3a , cis- 3a , and 13a in 61, 21, and 3% yield, respectively (Scheme 3). The stereoisomers trans- 3a and cis- 3a are the products of a regioselective 1,3-dipolar cycloaddition of carbonylylide 2b , generated thermally by an electrocyclic ring opening of 4b (Scheme 6), and the C?S group of 1a . Surprisingly, 13a proved not to be a regioisomeric cycloadduct of 1a and 2b , but an isomer formed via cleavage of the O? C(3) bond of the oxirane 4b . A reaction mechanism rationalizing the formation of 13a is proposed in Scheme 6. Analogous results were obtained from the reaction of 4b and 4,4-dimethyl-2-phenyl-1,3-thiazole-5 (4H)-thione ( 1b , Scheme 3). The thermolysis of 4b in p-xylene at 130° in the presence of adamantine–thione ( 10 ) led to two isomeric 1:1 adducts 15 and 16 in a ratio of ca. 2:1, however, in low yield (Scheme 4). Most likely the products are again formed viathe two competing reaction mechanisms depicted in Scheme 6. The analogous reactions of 4b with 2,2,4,4-tetramethylcyclobutane-1,3-thione ( 11 ) and 9H-xanthene-9-thione ( 12 ) yielded a single 1:1 adduct in each case (Schemes). In the former case, spirocyclic 1,3-oxathiolane 17 , the product of the 1,3-dipolar cycloaddition with 2a corresponding to 3a , was isolated in only 11 % yield. It is remarkable that no 2:1 adduct was formed even in the presence of an excess of 4b. In contrast, 4b and 12 reacted smoothly to give 18 in 81 % yield; no cycloadduct of the carbonylylide 2a could be detected. The structures of cis- 3a , 13a , 15 , and 18 , as well as the structure of 14 , which is a derivative of trans- 3a , have been established by X-ray crystallography (Figs. 1–3, Table).     

Thiocarbonyl-imide aus der Umsetzung von 2,2,4,4-Tetramethyl-3-thioxocyclobutanon mit Aryl-aziden

Thiocarbonyl Imides from the Reaction of 2,2,4,4-Tetramethyl-3-thioxocylobutanone and Aryl Azides Reaction of 2,2,4,4-tetramethyl-3-thioxocylobutanone ( 6 ) and 4-methoxyphenyl, phenyl, and 4-nitrophenyl azide ( 7a–c , respectively), at 80°, leads to the 11-aryl-5,10-dithia-11-azadispiro[3.1.3.2]undecane-2,8-diones 8a–c (Scheme 3), respectively, in 67–83% yield. The structure of 8b has been established by X-ray crystallography. The formation of the products may be explained via an intermediate thiocarbonyl imide of type D (Scheme 4), generated by the 1,3-dipolar cycloaddition of the aryl azide with the C? S bond of 6 and elimination of N₂.     

Hetero-Diels-Alder-Reaktion mit 1,3-Thiazol-5(4H)-thionen

Hetro-Diels-Alder Reaction with 1,3-Thiazol-5(4H)-thiones On heating in toluene to 180° and on treatment with BF₃·Et₂O in CH₂Cl₂ room temperature, 1,3-dienes react with the C?S group of 1,3-thiazol-5(4H)-thiones 1 in a reversible Diels-Alder reaction to give spiro[4.5]-heterocycles of type 6. A 1:1 mixture of two regioisomeric cycloadducts is formed in the thermal reaction with 2-methylbuta-1,3-diene (isoprene, 5b ). In contrast, the formation of one regioisomer is strongly preferred in the BF₃-catalyzed reaction. Frontier-orbital control as well as steric factors seem to be responsible for the observed regioselectivity. BF₃-Catalyzed, cyclic 1,3-dienes and 1 also undergo a smooth Diels-Alder reaction. Whereas cyclohexa-1,3-diene ( 5c ) reacts with 1a and 1b to give a single isomer (presumably the ‘exo’-adduct), cyclopenta-1,3-diene ( 5d ) leads to a ca. 3:1 mixture of ‘exo’-and ‘endo’-isomer.     

[2+3] Cycloadditions of ‘Thiocarbonyl Ylides’ (= (Alkylidenesulfonio)methanides) and diazoalkanes with N,N′-(thiocarbonyl)diimidazole (= 1,1′-(carbonothioyl)bis[1H-imidazole])

Heating of a mixture of N,N′-(thiocarbonyl)diimidazole (= 1,1′-(carbonothioyl)bis[1H-imidazole]; 1 ) and 2,5-dihydro-1,3,4-thiadiazole 2a or 2b gave the 1,3-dithiolanes 4a and 4b , respectively, via a regiospecific 1,3-dipolar cycloaddition of the corresponding ‘thiocarbonyl methanides’ 3a , b onto the C?S group of 1 (Schemes 1 and 2). The adamantane derivative 4b was not stable in the presence of 1H-imidazole and during chromatographic workup. The isolated 1,3-dithiole 5 is the product of a base-catalyzed elimination of 1H-imidazole from the initial cycloadduct 4b . The formation of the S,N-acetal 6 can be rationalized by a protonation of the ‘thiocarbonyl ylide’ 3b followed by a nucleophilic addition of 1H-imidazole. With the diazo compounds 8a–e (Scheme 3) 1 underwent a regiospecific 1,3-dipolar cycloaddition to give the corresponding 2,5-dihydro-1,3,4-thiadiazole derivatives 9 , which spontaneously eliminated 1H-imidazole to yield (1H-imidazol-1-yl)-1,3,4-thiadiazoles 10 . The structures of 10a and 10d were established by X-ray crystallography. In the case of diazodiphenylmethane ( 8f ), the initial cycloadduct 9f decomposed via a ‘twofold extrusion’ of N₂ and S to give 1,1′-(2,2-diphenylethenylidene)bis[1H-imidazole] ( 11 ; Scheme 3).     

Chemoselectivity of the Reactions of Diazomethanes with 5‐Benzylidene‐3‐phenylrhodanine

The reactions of 5‐benzylidene‐3‐phenylrhodanine ( 2 ; rhodanine=2‐thioxo‐1,3‐thiazolidin‐4‐one) with diazomethane ( 7a ) and phenyldiazomethane ( 7b ) occurred chemoselectively at the exocyclic C?C bond to give the spirocyclopropane derivatives 9 and, in the case of 7a , also the C‐methylated products 8 (Scheme 1). In contrast, diphenyldiazomethane ( 7c ) reacted exclusively with the C?S group leading to the 2‐(diphenylmethylidene)‐1,3‐thiazolidine 11 via [2+3] cycloaddition and a ‘two‐fold extrusion reaction’. Treatment of 8 or 9b with an excess of 7a in refluxing CH₂Cl₂ and in THF at room temperature in the presence of [Rh₂(OAc)₄], respectively, led to the 1,3‐thiazolidine‐2,4‐diones 15 and 20 , respectively, i.e., the products of the hydrolysis of the intermediate thiocarbonyl ylide. On the other hand, the reactions with 7b and 7c in boiling toluene yielded the corresponding 2‐methylidene derivatives 16, 21a , and 21b . Finally, the reaction of 11 with 7a occurred exclusively at the electron‐poor C?C bond, which is conjugated with the C?O group. In addition to the spirocyclopropane 23 , the C‐methylated 22 was formed as a minor product. The structures of the products (Z)‐ 8, 9a, 9b, 11 , and 23 were established by X‐ray crystallography.     

Reaktion von 3-(Dimethylamino)-2H-azirinen mit 1,3-Thiazolidin-2-thion

Reaction of 3-(Dimethylamino)-2H-azirines with 1,3-Thiazolidine-2-thione Reaction of 3-(dimethylamino)-2H-azirines 1 and 1,3-thiazolidine-2-thione ( 6 ) in MeCN at room temperature leads to a mixture of perhydroimidazo[4,3-b]thiazole-5-thiones 7 and N-[1-(4,5-dihydro-1,3-thiazol-2-yl)alkyl]-N′,N′-dimethylthioureas 8 (Scheme 2), whereas, in i-PrOH at ca. 60°, 8 is the only product (Scheme 4). It has been shown that, in polar solvents or under Me₂NH catalysis, the primarily formed 7 isomerizes to 8 (Scheme 4). The hydrolysis of 7 and 8 leads to the same 2-thiohydantoine 9 (Scheme 3 and 5). The structure of 7a, 8c , and 9b has been established by X-ray crystallography (Chapt. 4). Reaction mechanisms for the formation and the hydrolysis of 7 and 8 are suggested.     

Reactions of Stable α‐Chlorosulfanyl Chlorides with CS‐Functionalized Compounds

The smooth reaction of 3‐chloro‐3‐(chlorosulfanyl)‐2,2,4,4‐tetramethylcyclobutanone ( 3 ) with 3,4,5‐trisubstituted 2,3‐dihydro‐1H‐imidazole‐2‐thiones 8 and 2‐thiouracil ( 10 ) in CH₂Cl₂/Et₃N at room temperature yielded the corresponding disulfanes 9 and 11 (Scheme 2), respectively, via a nucleophilic substitution of Cl^? of the sulfanyl chloride by the S‐atom of the heterocyclic thione. The analogous reaction of 3‐cyclohexyl‐2,3‐dihydro‐4,5‐diphenyl‐1H‐imidazole‐2‐thione ( 8b ) and 10 with the chlorodisulfanyl derivative 16 led to the corresponding trisulfanes 17 and 18 (Scheme 4), respectively. On the other hand, the reaction of 3 and 4,4‐dimethyl‐2‐phenyl‐1,3‐thiazole‐5(4H)‐thione ( 12 ) in CH₂Cl₂ gave only 4,4‐dimethyl‐2‐phenyl‐1,3‐thiazol‐5(4H)‐one ( 13 ) and the trithioorthoester derivative 14 , a bis‐disulfane, in low yield (Scheme 3). At ?78°, only bis(1‐chloro‐2,2,4,4‐tetramethyl‐3‐oxocyclobutyl)polysulfanes 15 were formed. Even at ?78°, a 1 : 2 mixture of 12 and 16 in CH₂Cl₂ reacted to give 13 and the symmetrical pentasulfane 19 in good yield (Scheme 5). The structures of 11, 14, 17 , and 18 have been established by X‐ray crystallography.     

Erstes Beispiel einer H-Verschiebung in ‘Thiocarbonyl-aminiden’ (N-(Alkylidensulfonio)aminiden)

First Example of an H-Shift in ‘Thiocarbonyl Aminides’ (N-(Alkylidenesulfonio)aminides) Reaction of benzyl azide ( 15a ) with the sterically hindered C?S group of 4,4-dimethyl-1,3-thiazole-5(4H)-thiones 14 (Scheme 3) and 1,1,3,3-tetramethylindane-2-thione ( 17 , Scheme 4) at 80° leads to the corresponding imines in high yield, without formation of any by-product. In contrast, 15a and 2,2,4,4-tetramethyl-3-thioxocyclobutanone ( 7 ) under the same conditions yielded, in addition to imine 19 , products 20a and 21 (Scheme 5). For the formation of 20a , a reaction mechanism via [1,4]-H shift in the intermediate ‘thiocarbonyl aminides’ 23 is proposed (Scheme 6). Product 21 as well as the dithiazole derivative 22 , which is formed only in the reaction with 4-nitrobenzyl azide ( 15c ), are formal adducts of the dipole 23 . Whereas precedents are known for the formation of cycloadducts of type 22 , the pathway to 21 is not known. Two possible mechanisms of its formation are proposed in Schemes 8 and 9.     

Reaction of Optically Active Oxiranes with Thiofenchone and 1‐Methylpyrrolidine‐2‐thione: Formation of 1,3‐Oxathiolanes and Thiiranes

The SnCl₄‐catalyzed reaction of (?)‐thiofenchone (=1,3,3‐trimethylbicyclo[2.2.1]heptane‐2‐thione; 10 ) with (R)‐2‐phenyloxirane ((R)‐ 11 ) in anhydrous CH₂Cl₂ at ?60° led to two spirocyclic, stereoisomeric 4‐phenyl‐1,3‐oxathiolanes 12 and 13 via a regioselective ring enlargement, in accordance with previously reported reactions of oxiranes with thioketones (Scheme 3). The structure and configuration of the major isomer 12 were determined by X‐ray crystallography. On the other hand, the reaction of 1‐methylpyrrolidine‐2‐thione ( 14a ) with (R)‐ 11 yielded stereoselectively (S)‐2‐phenylthiirane ((S)‐ 15 ) in 56% yield and 87–93% ee, together with 1‐methylpyrrolidin‐2‐one ( 14b ). This transformation occurs via an S_N2‐type attack of the S‐atom at C(2) of the aryl‐substituted oxirane and, therefore, with inversion of the configuration (Scheme 4). The analogous reaction of 14a with (R)‐2‐{[(triphenylmethyl)oxy]methyl}oxirane ((R)‐ 16b ) led to the corresponding (R)‐configured thiirane (R)‐ 17b (Scheme 5); its structure and configuration were also determined by X‐ray crystallography. A mechanism via initial ring opening by attack at C(3) of the alkyl‐substituted oxirane, with retention of the configuration, and subsequent decomposition of the formed 1,3‐oxathiolane with inversion of the configuration is proposed (Scheme 5).     

Diazo-Transfer Reaction with Diphenyl Phosphorazidate

Diphenyl phosphorazidate (DPPA) was used as the azide source in a one-pot synthesis of 2,2-disubstituted 3-amino-2H-azirines 1 (Scheme 1). The reaction with lithium enolates of amides of type 2 , bearing two substituents at C(2), proceeded smoothly in THF at 0°; keteniminium azides C and azidoenamines D are likely intermediates. Under analogous reaction conditions, DPPA and amides of type 3 with only one substituent at C(2) gave 2-diazoamides 5 in fair-to-good yield (Scheme 2). The corresponding 2-diazo derivatives 6–8 were formed in low yield by treatment of the lithium enolates of N,N-dimethyl-2-phenylacetamide, methyl 2-phenylacetate, and benzyl phenyl ketone, respectively, with DPPA. Thermolysis of 2-diazo-N-methyl-N-phenylcarboxamides 5a and 5b yielded 3-substituted 1,3-dihydro-N-methyl-2H-indol-2-ones 9a and 9b , respectively (Scheme 3). The diazo compounds 5–8 reacted with 1,3-thiazole-5 (4H)-thiones 10 and thiobenzophenone ( 13 ) to give 6-oxa-1,9-dithia-3-azaspiro[4.4]nona-2,7-dienes 11 (Scheme 4) and thiirane-2-carboxylic acid derivatives 14 (Scheme 5), respectively. In analogy to previously described reactions, a mechanism via 1,3-dipolar cycloaddition, leading to 2,5-dihydro-1,3,4-thiadiazoles, and elimination of N₂ to give the ‘thiocarbonyl ylides’ of type H or K is proposed. These dipolar intermediates with a conjugated C?O group then undergo either a 1,5-dipolar electrocyclization to give spirohetrocycles 11 or a 1,3-dipolar electrocyclization to thiiranes 14 .     

Synthese von Trifluoromethyl-substituierten Schwefel-Heterocyclen unter Verwendung von 3,3,3-Trifluorobrenztraubensäure-Derivaten

Synthesis of Trifluoromethyl-Substituted Sulfur Heterocycles Using 3,3,3-Trifluoropyruvic-Acid Derivatives The reaction of methyl 3,3,3-trifluoropyruvate ( 1 ) with 2,5-dihydro-1,3,4-thiadiazoles 4a, b in benzene at 45° yielded the corresponding methyl 5-(trifluoromethyl)-1,3-oxathiolane-5-carboxylates 5a, b (Scheme 1) via a regioselective 1,3-dipolar cycloaddition of an intermediate ‘thiocarbonyl ylide’ of type 3 . With methyl pyruvate, 4a reacted similarly to give 6 in good yield. Methyl 2-diazo-3,3,3-trifluoropropanoate ( 2 ) and thiobenzophenone ( 7a ) in toluene underwent a reaction at 50°; the only product detected in the reaction mixture was thiirane 8a (Scheme 2). With the less reactive thiocarbonyl compounds 9H-xanthene-9-thione ( 7b ) and 9H-thioxanthene-9-thione ( 7c ) as well as with 1,3-thiazole-5(4H)-thione 12 , diazo compound 2 reacted only in the presence of catalytic amounts of Rh₂(OAc)₄. In the cases of 7a and 7b , thiiranes 8b and 8c , respectively, were the sole products (Scheme 3). The crystal struture of 8c has been established by X-ray crystallography (Fig.). In the reaction with 12 , desulfurization of the primarily formed thiirane 14 gave the methyl 3,3,3-trifluoro-2-(4,5-dihydro-1,3-thiazol-5-ylidene)propanoates (E)-and (Z)- 15 (Scheme 4). A mechanism of the Rh-catalyzed reaction via a carbene addition to the thiocarbonyl S-atom is proposed in Scheme 5.     

Light-Induced,Thermal, and Acid-Catalyzed π-Skeletal Rearrangements of Five-Ring-Annelated Heptalenes

It is shown that, upon irradiation in CDCl₃ solution, 5,6,8,10-tetramethylheptalene-1,2-dicarboxylic anhydride ( 6 ) rearranges to its double-bond-shift (DBS) isomer 7 in an equilibrium reaction (Scheme 2). The isomer 7 is DBS stable at ?50°. At ca. 30°, a thermal equilibrium with 97.8% of 6 and 2.2% of 7 is rapidly established. Similarly, the ‘ortho’-anhydrides 9 and 11 (Schemes 4 and 5) can be rearranged to their corresponding DBS isomers 12 and 13 , respectively. Whereas 12 is DBS stable at 30° (at 100° in tetralin, 94.0% of 9 are in equilibrium with 6.0% of 12 ), the i-Pr-substituted isomer 13 is already at 30° in thermal equilibrium with 11 leading to 98.7% of 11 and 1.3% of 13 . It is shown by rearrangement of diasteroisomeric ‘ortho’-anhydrides of known relative and absolute configuration (Scheme 6) that the DBS in such five-ring-annelated heptalenes occurs with retention of the configuration of the heptalene skeleton as already established for other heptalene compounds. It is found that the DBS process may also take place under acid catalysis (e.g. HCl/CH₃OH), thus yielding 9 from 12 (Scheme 9). The ‘ortho’-anhydrides 21 and 23 (Scheme 10) which are isomeric with 9 and 11 (Scheme 3) undergo rapid DBS' already at room temperature. The thermal equilibrium 21?22 consists of 18% of 21 and 82% of 22 at 30° and that of 23?24 of 17% of 23 and 83% of 24 at ?30°. From these equilibrium mixtures, the pure DBS isomer 22 can be obtained by crystallization. Again, these rapid DBS' occur with retention of configuration of the heptalene skeleton (Fig. 4).     

4-Amino-1,5-dihydro-2H-pyrrol-2-one aus Bortrifluorid-katalysierten Umsetzungen von 3-Amino-2H-azirinen mit Carbonsäure-Derivaten

4-Amino-1,5-dihydro-2H-pyrrol-2-ones from Boron Trifluoride Catalyzed Reactions of 3-Amino-2H-azirines with Carboxylic Acid Derivatives Reaction of 3-amino-2H-azirines 1 with ethyl 2-nitroacetate ( 6a ) in refluxing MeCN affords 4-amino-1,5-dihydro-2H-pyrrol-2-ones 7 and 3,6-diamino-2,5-dihydropyrazines 8 , the dimerization product of 1 (Scheme 2). Thus, 6a reacts with 1 as a CH-acidic compound by C? C bond formation via C-nucleophilic attack of deprotonated 6a onto the amidinium-C-atom of protonated 1 (Scheme 5). The scope of this reaction seems to be rather limited as 1 and 2-substituted 2-nitroacetates do not give any products besides the azirine dimer 8 (see Table 1). Sodium enolates of carboxylic esters and carboxamides 11 react with 1 under BF₃ catalysis to give 4-amino-1,5-dihydro-2H-pyrrol-2-ones 12 in 50–80% yield (Scheme 3, Table 2). In an analogous reaction, 3-amino-2H-pyrrole 13 is formed from 1c and the Li-enolate of acetophenone (Scheme 4). A reaction mechanism for the ring enlargement of 1 involving BF₃ catalysis is proposed in Scheme 6.     

1,5-Dipolare Elektrocyclisierung von Acyl-substituierten ‘Thiocarbonyl-yliden’ zu 1,3-Oxathiolen

1,5-Dipolar Electrocyclization of Acyl-Substituted ‘Thiocarbonyl-ylides’ to 1,3-Oxathioles The reaction of α-diazoketones 15a, b with 4,4-disubstituted 1,3-thiazole-5(4H)-thiones 6 (Scheme 3), adamantanethione ( 17 ), 2,2,4,4-tetramethyl-3-thioxocyclobutanone ( 19 ; Scheme 4), and thiobenzophenone ( 22 ; Scheme 5), respectively, at 50–90° gave the corresponding 1,3-oxathiole derivatives as the sole products in high yields. This reaction opens a convenient access to this type of five-membered heterocycles. The structures of three of the products, namely 16c, 16f , and 20b , were established by X-ray crystallography. The key-step of the proposed reaction mechanism is a 1,5-dipolar electrocyclization of an acyl-substituted ‘thiocarbonyl-ylide’ (cf. Scheme 6). The analogous reaction of 15a, b with 9H-xanthen-9-thione ( 24a ) and 9H-thioxanthen-9-thione ( 24b ) yielded α,β-unsaturated ketones of type 25 (Scheme 5). The structures of 25a and 25c were also established by X-ray crystallography. The formation of 25 proceeds via a 1,3-dipolar electrocyclization to a thiirane intermediate (Scheme 6) and desulfurization. From the reaction of 15a with 24b in THF at 50°, the intermediate 26 (Scheme 5) was isolated. In the crude mixtures of the reactions of 15a with 17 and 19 , a minor product containing a CHO group was observed by IR and NMR spectroscopy. In the case of 19 , this side product could be isolated and was characterized by X-ray crystallography to be 21 (Scheme 4). It was shown that 21 is formed – in relatively low yield – from 20a . Formally, the transformation is an oxidative cleavage of the C?C bond, but the reaction mechanism is still not known.     

Umsetzung von Di(tert-butyl)- und Diphenyldiazomethan mit 1,3-Thiazol-5(4H)-thionen: Isolierung und Kristallstruktur des primären Cycloadduktes

Reaction of Di(tert-butyl)- and Diphenyldiazomethane and 1,3-Thiazole-5(4H)-thiones: Isolation and Crystal Structure of the Primary Cycloadduct Reactions of diazo compounds with C?S bonds proceed via the formation of thiocarbonyl ylides, which, under the reaction conditions, undergo either 1,3-dipolar cycloadditions or electrocyclic ring closer to thiiranes (Scheme 1). With the sterically hindered di(tert-butyl)diazomethane ( 2c ), 1,3-thiazole-5(4H)-thiones 1 react to give spirocyclic 2,5-dihydro-1,3,4-thiadiazoles 3 (Scheme 2). These adducts are stable in solution at ?20°, and they could be isolated in crystalline form. The structure of 3c was established by X-ray crystallography. In CDCl₃ solution at room temperature, a cycloreversion occurs, and the adducts of type 3 are in an equilibrium with 1 and 2c . In contrast, the reaction of 1 with diphenyldiazomethane ( 2d ) gave spirocyclic thiiranes 4 as the only product in high yield (Scheme 3). The crystal structure of 4b was also determined by X-ray analysis. The desulfurization of compounds 4 to 4,5-dihydro-5-(diphenylmethylidene)-1,3-thiazoles 5 was achieved by treating 4 with triphenylphosphine in boiling THF. The crystal structure of 5f is shown.