1,3-Oxathiole and Thiirane Derivatives from the Reactions of Azibenzil and α-diazo amides with thiocarbonyl compounds

The reactions of α-diazo ketones 1a,b with 9H-fluorene-9-thione ( 2f ) in THF at room temperature yielded the symmetrical 1,3-dithiolanes 7a,b , whereas 1b and 2,2,4,4-tetramethylcyclobutane-1,3-dithione ( 2d ) in THF at 60° led to a mixture of two stereoisomeric 1,3-oxathiole derivatives cis- and trans- 9a (Scheme 2). With 2-diazo-1,2-diphenylethanone ( 1c ), thio ketones 2a–d as well as 1,3-thiazole-5(4H)-thione 2g reacted to give 1,3-oxathiole derivatives exclusively (Schemes 3 and 4). As the reactions with 1c were more sluggish than those with 1a,b , they were catalyzed either by the addition of LiClO₄ or by Rh₂(OAc)₄. In the case of 2d in THF/LiClO₄ at room temperature, a mixture of the monoadduct 4d and the stereoisomeric bis-adducts cis- and trans- 9b was formed. Monoadduct 4d could be transformed to cis- and trans- 9b by treatment with 1c in the presence of Rh₂(OAc)₄ (Scheme 4). Xanthione ( 2e ) and 1c in THF at room temperature reacted only when catalyzed with Rh₂(OAc)₄, and, in contrast to the previous reactions, the benzoyl-substituted thiirane derivative 5a was the sole product (Scheme 4). Both types of reaction were observed with α-diazo amides 1d,e (Schemes 5–7). It is worth mentioning that formation of 1,3-oxathiole or thiirane is not only dependent on the type of the carbonyl compound 2 but also on the α-diazo amide. In the case of 1d and thioxocyclobutanone 2c in THF at room temperature, the primary cycloadduct 12 was the main product. Heating the mixture to 60°, 1,3-oxathiole 10d as well as the spirocyclic thiirane-carboxamide 11b were formed. Thiirane-carboxamides 11d–g were desulfurized with (Me₂N)₃P in THF at 60°, yielding the corresponding acrylamide derivatives (Scheme 7). All reactions are rationalized by a mechanism via initial formation of acyl-substituted thiocarbonyl ylides which undergo either a 1,5-dipolar electrocyclization to give 1,3-oxathiole derivatives or a 1,3-dipolar electrocyclization to yield thiiranes. Only in the case of the most reactive 9H-fluorene-9-thione ( 2f ) is the thiocarbonyl ylide trapped by a second molecule of 2f to give 1,3-dithiolane derivatives by a 1,3-dipolar cycloaddition.     

Unexpected Formation of Dimethylthioketene Cycloadducts in the Reaction of 1,3‐Diphenylaziridine‐2,2‐dicarboxylate with Cyclobutanethione Derivatives

The reaction of 2,2,4,4‐tetramethyl‐3‐thioxocyclobutanone ( 1 ) with cis‐1‐alkyl‐2,3‐diphenylaziridines 5 in boiling toluene yielded the expected trans‐configured spirocyclic 1,3‐thiazolidines 6 (Scheme 1). Analogously, dimethyl trans‐1‐(4‐methoxyphenyl)aziridine‐2,3‐dicarboxylate (trans‐ 7 ) reacted with 1 and the corresponding dithione 2 , respectively, to give spirocyclic 1,3‐thiazolidine‐2,4‐dicarboxylates 8 (Scheme 2). However, mixtures of cis‐ and trans‐derivatives were obtained in these cases. Unexpectedly, the reaction of 1 with dimethyl 1,3‐diphenylaziridine‐2,2‐dicarboxylate ( 11 ) led to a mixture of the cycloadduct 13 and 5‐(isopropylidene)‐4‐phenyl‐1,3‐thiazolidine‐2,2‐dicarboxylate ( 14 ), a formal cycloadduct of azomethine ylide 12 with dimethylthioketene (Scheme 3). The regioisomeric adduct 16 was obtained from the reaction between 2 and 11 . The structures of 6b , cis‐ 8a , cis‐ 8b, 10 , and 16 have been established by X‐ray crystallography.     

Reaktion von Phenyldiazomethan mit 1,3-Thiazol-5(4H)-thionen: Basenkatalysierte Ring-Öffnung des Primäradduktes

Reaction of Phenyldiazomethane with 1,3-Thiazole-5(4H)-thiones: Base-Catalyzed Ring Opening of the Primary Adduct Reaction of 1,3-thiazole-5(4H)-thiones 1 and phenyldiazomethane ( 2a ) in toluene at room temperature yields the thiiranes trans- and cis-1,4-dithia-6-azaspiro[2.4]hept-5-enes (trans- and cis- 4 ; Scheme 2). With Ph₃P in THF at 70°, these thiiranes are transformed stereospecifically into (E)- and (Z)-5-benzylidene-4,5-dihydro-1,3-thiazoles 5 , respectively. In the presence of DBU, 1 and 2a react to give 1,3,4-thiadiazole derivatives 6 or 7 via base-catalyzed ring opening of the primary cycloadduct (Scheme 3). In the case of 2-(alkylthio)-substituted 1,3-thiazole-5(4H)-thiones 1c and 1d , this ring opening proceeds by elimination of the corresponding alkylthiolate, yielding isothiocyanate 7 . The structures of (Z)- 5c and 6b have been established by X-ray crystallography.     

1,3‐Thiazolidine‐dicarboxylates from Thioketones and Thermally Generated Azomethine Ylides

The reaction of 9H‐fluorene‐9‐thione ( 1 ) with the cis‐ and trans‐isomers of dimethyl 1‐(4‐methoxyphenyl)aziridine‐2,3‐dicarboxylate (cis‐ and trans‐ 2 , resp.) in xylene at 110° yielded exclusively the spirocyclic cycloadduct with trans‐ and cis‐configurations, respectively (trans‐ and cis‐ 3 , resp.; Scheme 1). Analogously, less‐reactive thioketones, e.g., thiobenzophenone ( 5 ), and cis‐ 2 reacted stereoselectively to give the corresponding trans‐1,3‐thiazolidine‐2,4‐dicarboxylate (e.g., trans‐ 8 ; Scheme 2). On the other hand, the reaction of 5 and trans‐ 2 proceeded in a nonstereoselective course to provide a mixture of trans‐ and cis‐substituted cycloadducts. This result can be explained by an isomerization of the intermediate azomethine ylide. Dimethyl 1,3‐thiazolidine‐2,2‐dicarboxylates 14 and 15 were formed in the thermal reaction of dimethyl aziridine‐2,2‐dicarboxylate 11 with aromatic thioketones (Scheme 3). On treatment of 14 and 15 with Raney‐Ni in refluxing EtOH, a desulfurization and ring‐contraction led to the formation of azetidine‐2,2‐dicarboxylates 17 and 18 , respectively (Scheme 4).     

New Studies on [2+3] Cycloadditions of Thermally Generated N‐Isopropyl‐ and N‐(4‐Methoxyphenyl)‐Substituted Azomethine Ylides

The thermal reaction of 1‐substituted 2,3‐diphenylaziridines 2 with thiobenzophenone ( 6a ) and 9H‐fluorene‐9‐thione ( 6b ) led to the corresponding 1,3‐thiazolidines (Scheme 2). Whereas the cis‐disubstituted aziridines and 6a yielded only trans‐2,4,5,5‐tetraphenyl‐1,3‐thiazolidines of type 7 , the analogous reaction with 6b gave a mixture of trans‐ and cis‐2,4‐diphenyl‐1,3‐thiazolidines 7 and 8 . During chromatography on SiO₂, the trans‐configured spiro[9H‐fluorene‐9,5′‐[1,3]thiazolidines] 7c and 7d isomerized to the cis‐isomers. The substituent at N(1) of the aziridine influences the reaction rate significantly, i.e., the more sterically demanding the substituent the slower the reaction. The reaction of cis‐2,3‐diphenylaziridines 2 with dimethyl azodicarboxylate ( 9 ) and dimethyl acetylenedicarboxylate ( 11 ) gave the trans‐cycloadducts 10 and 12 , respectively (Schemes 3 and 4). In the latter case, a partial dehydrogenation led to the corresponding pyrroles. Two stereoisomeric cycloadducts, 15 and 16 , with a trans‐relationship of the Ph groups were obtained from the reaction with dimethyl fumarate ( 14 ; Scheme 5); with dimethyl maleate ( 17 ), the expected cycloadduct 18 together with the 2,3‐dihydropyrrole 19 was obtained (Scheme 6). The structures of the cycloadducts 7b, 8a, 15b , and 16b were established by X‐ray crystallography.     

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 .     

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.     

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.     

Reaktionen von 3-(Dimethylamino)-2H-azirinen mit 1,3-Benzoxazol-2(3H)-thion

Reaction of 3-(Dimethylamino)-2H-azirines with 1,3-Benzoxazole-2(3H)-thione The reaction of 3-(dimethylamino)-2H-azirines 2 with 1,3-benzoxazole-2(3H)-thione ( 5 ), which can be considered as NH-acidic heterocycle (pK_aca. 7.3), in MeCN at room temperature, leads to 3-(2-hydroxyphenyl)-2-thiohydantoins 6 and thiourea derivatives of type 7 (Scheme 2). A reaction mechanism for the formation of the products via the crucial zwitterionic intermediate A ′ is suggested. This intermediate was trapped by methylation with Mel and hydrolysis to give 9 (Scheme 4). Under normal reaction conditions, A ′ undergoes a ring opening to B which is hydrolyzed during workup to yield 6 or rearranges to give the thiourea 7. A reasonable intermediate of the latter transformation is the isothiocyanate E (Scheme 3) which also could be trapped by morpholine. In i-PrOH at 55–65° 2a and 5 react to yield a mixture of 6a , 2-(isopropylthio)-1,3-benzoxazole ( 12 ), and the thioamide 13 (Scheme 5). A mechanism for the surprising alkylation of 5 via the intermediate 2-amino-2-alkoxyaziridine F is proposed. Again via an aziridine, e.g. H ( Scheme 6 ), the formation of 13 can be explained.     

Synthesis of 4-Alkoxy-1,3-oxazol-5(2H)-ones,Precursors of 1-alkoxy substituted nitrile ylides

4-Alkoxy-1,3-oxazol-5(2H)-ones of type 4 and 7 were synthesized by two different methods: oxidation of the 4-(phenylthio)-1,3-oxazol-5(2H)-one 2a with m-chloroperbenzoic acid in the presence of an alcohol gave the corresponding 4-alkoxy derivatives 4 , presumably via nucleophilic substitution of an intermediate sulfoxide (Scheme 2). The second approach is the BF₃-catalyzed condensation of imino-acetates of type 6 and ketones (Scheme 3). The yields of this more straightforward method were modest due to the competitive formation of 1,3,5-triazine tricarboxylate 8. At 155°, 1,3-oxazol-5(2H)-one 7b underwent decarboxylation leading to an alkoxy-substituted nitrile ylide which was trapped in a 1,3-dipolar cycloaddition by trifluoro-acetophenone to give the dihydro-oxazoles cis- and trans- 9 (Scheme 4). In the absence of a dipolarophile, 1,5-dipolar cyclization of the intermediate nitrile ylide yielded isoindole derivatives 10 (Schemes 4 and 5).     

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.     

N-(1,3-Thiazol-5(4H)-yliden)amine aus 1,3-dipolaren Cycloadditionen von Aziden mit 1,3-Thiazol-5(4H)-thionen

N-(1,3-Thiazol-5(4H)-ylidene)amines via 1,3-Dipolar Cycloaddition of Azides and 1,3-Thiazol-5(4H)-thiones Organic azides 5 and 4,4-dimethyl-2-phenyl-1,3-thiazol-5(4H)-thione ( 2 ) in toluene at 90° react to give the corresponding N-(1,3-thiazol-5(4H)-ylidene)amines (= 1,3-thiazol-5(4H)-imines) 6 in good yield (Table). A reaction mechanism for the formation of these scarcely investigated thiazole derivatives is formulated in Scheme 3: 1,3-Dipolar azide cycloaddition onto the C?S group of 2 leads to the 1:1 adduct C . Successive elimination of N₂ and S yields 6 , probably via an intermediate thiaziridine E .     

Thermal [2+3]‐Cycloadditions of trans‐1‐Methyl‐2,3‐diphenylaziridine with CS and CC Dipolarophiles: An Unexpected Course with Dimethyl Dicyanofumarate

The thermal reaction of trans‐1‐methyl‐2,3‐diphenylaziridine (trans‐ 1a ) with aromatic and cycloaliphatic thioketones 2 in boiling toluene yielded the corresponding cis‐2,4‐diphenyl‐1,3‐thiazolidines cis‐ 4 via conrotatory ring opening of trans‐ 1a and a concerted [2+3]‐cycloaddition of the intermediate (E,E)‐configured azomethine ylide 3a (Scheme 1). The analogous reaction of cis‐ 1a with dimethyl acetylenedicarboxylate ( 5 ) gave dimethyl trans‐2,5‐dihydro‐1‐methyl‐2,5‐diphenylpyrrole‐3,4‐dicarboxylate (trans‐ 6 ) in accord with orbital‐symmetry‐controlled reactions (Scheme 2). On the other hand, the reactions of cis‐ 1a and trans‐ 1a with dimethyl dicyanofumarate ( 7a ), as well as that of cis‐ 1a and dimethyl dicyanomaleate ( 7b ), led to mixtures of the same two stereoisomeric dimethyl 3,4‐dicyano‐1‐methyl‐2,5‐diphenylpyrrolidine‐3,4‐dicarboxylates 8a and 8b (Scheme 3). This result has to be explained via a stepwise reaction mechanism, in which the intermediate zwitterions 11a and 11b equilibrate (Scheme 6). In contrast, cis‐1,2,3‐triphenylaziridine (cis‐ 1b ) and 7a gave only one stereoisomeric pyrrolidine‐3,4‐dicarboxylate 10 , with the configuration expected on the basis of orbital‐symmetry control, i.e., via concerted reaction steps (Scheme 10). The configuration of 8a and 10 , as well as that of a derivative of 8b , were established by X‐ray crystallography.     

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 3-(Dimethylamino)-2H-azirinen mit 1,3-Oxazolidin-2-thion zu 3-(2-Hydroxyethyl)-2-thiohydantoinen

Reaction of 3-(Dimethylamino)-2H-azirines with 1,3-Oxazolidine-2-thione to 3-(2-Hydroxyethyl)-2- thiohydantoins The reaction of 3-(dimethylamino)-2H-azirines 1 and 1,3-oxazolidine-2-thione ( 6 ), in MeCN at room temperature, yields, after hydrolytic workup, 3-(2-hydroxyethyl)-2-thiohydantoins 7 (Scheme 2). In the case of the spirocyclic 1c , crystallization of the crude reaction mixture leads to spiro [cyclopentane-1, 7′(7′aH)-imidazo [4, 3-b] oxazole] -5′-thione 8c . The mechanism is discussed.     

1,3-Oxathiolan-Synthese: Spirocyclische 1,3-Oxathiolane aus der Lewis-Säure-katalysierten Umsetzung von cyclischen Trithiocarbonaten und Oxiranen

1,3-Oxathiolanc Synthesis: Spirocyclic 1,3-Oxathiolanes from the Lewis-Acid-Catalyzed Reaction of Cyclic Trithiocarbonates and Oxiranes The cyclic trithiocarbonates 1.3-dithiolane-2-thione ( 4 ) and 1,3-dithiole-2-thione ( 9 ) in 1,2-dichloroethane and MeCN, respectively, react with alkyl- and phenyl-substituted oxiranes 2 in the presence of Lewis acids to give 1-oxa-4,6,9-trithiaspiro[4.4]nonanes 5 and 6 (Scheme 2) and 1-oxa-4,6,9-trithiaspiro[4.4]non-7-enes 10 and 11 (Scheme 3), respectively. The reactions proceed regioselectively yielding 2-alkyl ( 5 , 10 ) and 3-phenyl derivatives ( 6 , 11 ) as the main products. From the reaction of 4 and 2-phenyloxirane ( 2e ) with TiCl₄, 2-phenyl-1,4,6,9-tetrathia-spiro[4.4]nonane ( 7 ) is isolated as a minor product. The molecular structures of 5a , 6e , and 7 are established by X-ray crystallography.     

1,3-Dipolare Cycloadditionen von 2-(Benzonitrilio)-2-propanid mit 4,4-Dimethyl-2-phenyl-2-thiazolin-5-thion und Schwefelkohlenstoff

1,3-Dipolar Cycloadditions of 2-(Benzonitrilio)-2-propanide with 4,4-Dimethyl-2-phenyl-2-thiazolin-5-thione and Carbon Disulfide Irradiation of 2,2-dimethyl-3-phenyl-2H-azirine ( 11 ) in the presence of 4,4-dimethyl-2-phenyl-2-thiazolin-5-thione ( 7 ) yields a mixture of the three (1:1)-ad-ducts 8 , 12 and 13 (Schemes 3 and 6). The formation of 8 and 12 can be explained by 1,3-dipolar cycloaddition of 2-(benzonitrilio)-2-propanide ( 1b ) to the C, S-double bond of 7. Photochemical isomerization of 12 leads to the third isomer 13 (Schemes 3 and 7). Photolysis of the azirine 11 in the presence of carbon disulfide gives a mixture of two (2:l)-adducts, namely 12 and 13 (Scheme 4). A reaction mechanism via the intermediate formation of the 3-thiazolin-5-thione b is postulated. The structure of the heterocyclic spiro compound 13 has been established by single-crystal X-ray structure determination (cf. Fig. 1 and 2).     

[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).     

1,3-Heterazolidines-2-heterounsaturated compounds derived from ephedrines

Herein, a direct and easy method for preparing 2-oxo-, 2-thione- or 2-imine-1,3-heterazolidines derived from ephedrines and norephedrines are reported. The method is based on solvent free heating of ephedrines with oxocyanate or thiocyanate salts (180–200 °C). In the reactions with potassium oxocyanate in refluxing ethanol, it was possible to isolate ureidic derivatives. The structure and stereochemistry of the compounds were determined by ¹H, ¹³C NMR, IR spectroscopies and mass spectrometry. Ureidic derivatives, cis-1,5-dimethyl-4-phenyl-imidazolidine-2-thione and trans-4-methyl-5-phenyl-thiazolidine-2-one are new compounds. Ephedrineurea, cis-1,5-dimethyl-4-phenyl-imidazolidine-2-thione and trans-4-methyl-5-phenyl-thiazolidine-2-one were also studied by X-ray diffraction.     

Stereospezifische Fragmentierungen in den Massenspektren von Cyclohexandiaminen und Bis(aminomethyl)cyclohexanen. 33. Mitteilung über massenspektrometrische Untersuchungen,,

Stereospecific Fragmentations in the Mass Spectra of Cyclohexanediamines and Bis(aminomethyl)cyclohexanes The mass spectral behaviour, especially loss of NH₃, of the six isomeric cyclohexanediamines 1--3 (cis and trans each, Scheme 1) as well as of the six isomeric bis(aminomethyl)cyclohexanes 4--6 (cis and trans each, Scheme 6) has been investigated. The cis- and trans-compounds of the 1,2-isomers 1 and 4 show very similar spectra, because of the ease of ring cleavage at C(1)–-C(2) and the similar geometrical relations in all ring conformations. The cis- and trans-compounds of both the 1,3- and 1,4-isomers 2, 3, 5 and 6 show striking differences in their mass spectra due to stereospecific elimination of NH₃ from the molecular ion.