Selective imidoylnitrenes

Two new imidoylnitrenes and alkoxycarbonylnitrene form a sequence of reactivities : Only ROCON attacks CH bonds, it and ROC(NCN)N convert benzene to azepines. Benzene is not attacked by ROC(NSO₂CH₃)N, but all three nitrenes react with olefins, alcohols, etc.     

A novel and simple route for the synthesis of 3,4‐disubstituted pyrroles

A new class of 3,4‐disubstituted pyrroles has been prepared by the reaction of 1‐aroyl‐2‐arylsul‐fonylethenes and 1,2‐diarylsulfonylethenes with tosyl methyl isocyanide.     

Asymmetric synthesis of 2,3-dihydrofurans and of unsaturated bicyclic tetrahydrofurans through alpha-elimination and migratory cyclization of silyloxy alkenyl aminosulfoxonium salts. Generation and intramolecular O,Si-bond insertion of chiral disubstituted beta-silyloxy alkylidene carbenes

Treatment of the bis(allylsulfoximine)titanium complexes derived from the beta-methyl-substituted acyclic allylic sulfoximines 13a and 13b with aldehydes gave with high selectivities the corresponding sulfoximine-substituted homoallylic alcohols which were isolated as the silyl ethers 15a-h. Methylation of sulfoximines 15a-h afforded the aminosulfoxonium salts 5a-h which upon treatment with LiN(H)tBu gave in high yields the enantio- and diastereomerically pure silyl-substituted 2,3-dihydrofurans 4a-h. Treatment of the titanium complexes derived from the cyclic allylic sulfoximines 17a, 17b, and ent-17c with p-MeOC(6)H(4)CHO delivered with high selectivities the corresponding sulfoximine-substituted cyclic homoallylic alcohols which were isolated as the silyl ethers 18a, 18b, and ent-18c, respectively. Methylation of sulfoximines 18a, 18b, and ent-18c furnished the aminosulfoxonium salts 8a, 8b, and ent-8c, respectively, whose treatment with LiN(H)t-Bu gave the enantio- and diastereomerically pure fused bicyclic 2,3-dihydrofurans 6a, 6b, and ent-6c, respectively, in good yields. It is proposed that the 1-alkenyl aminosulfoxonium salts 5a-h, 8a, 8b, and ent-8c react with the base under alpha-elimination and formation of the acyclic and cyclic beta-silyloxy alkylidene carbenes 2a-h, 7a, 7b, and ent-7c, respectively, which then undergo a 1,5-O,Si-bond insertion and 1,2-silyl migration. The cyclic aminosulfoxonium salts 8a, 8b, and ent-8c upon treatment with 1,8-diazabicyclo[5.4.0]-7-undecene did not undergo an alpha-elimination but suffered a novel migratory cyclization with formation of the enantio- and diastereomerically pure bicyclic tetrahydrofurans 9a, 9b, and ent-9c, respectively. It is proposed that the 1-alkenyl sulfoxonium salts 8a, 8b, and ent-8c are isomerized to the allylic aminosulfoxonium salts 10a, 10b, and ent-10c, respectively, which then suffer an intramolecular substitution of the (dimethylamino)sulfoxonium group by the silyloxy group followed by a desilylation. The syntheses of the 2,3-dihydrofurans 4a-h, 6a, and 6b and of the tetrahydrofurans 9a and 9b are accompanied by the formation of sulfinamide 16 of >or=98% ee, which can be converted via sulfoxide 28 of >or=98% to the starting sulfoximine 11 of >or=98% ee.     

13C NMR/DFT/GIAO studies of phenylene bis(1,3-dioxolanium) dications and 2,4,6-triphenylene tris(1,3-dioxolanium) trication

The o-, m-, and p-phenylene bis(1,3-dioxolanium) dications (4-6) and 2,4,6-triphenylene tris(1,3-dioxolanium) trication (7) have been prepared by the ionization of the corresponding 2-methoxyethyl benzoates in FSO(3)H or CF(3)SO(3)H at 40 and 60 degrees C, respectively. The charge delocalization in these carbocations was probed by (13)C NMR chemical shifts and substantiated by GIAO/DFT calculations. Relatively less charge is delocalized into the aromatic ring of the carbotrication 7. The rotational barrier around the C(+)-Ar bond for carbodications 4 and 5 was also estimated to be 8-10 kcal/mol.     

Sc(OTf)3-catalyzed alkylation of indoles with propargyl alcohols: an expeditious synthesis of 3-substituted indoles

Indoles undergo smooth alkylation with propargylic alcohols in the presence of 10 mol % of scandium triflate under mild conditions to produce 3-propargylated indoles in excellent yields with high selectivity.     

Synthesis and characterization of polyesters containing heterocyclic thiaxanthone units

Several polyesters containing thiaxanthone rings were prepared from 2,7-dichloroformylthiaxanthone-5,5′-dioxide ( IVa ), 2,8-dichloroformylthiaxanthone-5,5′-dioxide ( IVb ), and bisphenols by solution polycondensation. The 2,8-diethoxycarbonylthiaxanthone-5,5′-dioxide ( V ) was prepared and characterized by spectral methods to confirm the formation of 2,8-thiaxanthonedicarboxylic acid-5,5′-dioxide ( IVb ). Prior to polymer synthesis two model compounds,2,7-diphenoxycarbonylthiaxanthone-5,5′-dioxide (MDE-1) and 2,8-diphenoxycarbonylthiaxanthone-5,5′-dioxide (MDE-2), were synthesized and characterized by spectral methods. The polyesters were obtained in 62–78% yield and had inherent viscosities in the range 0.42–0.90 dL/g. The effect of thiaxanthone rings on solubility, crystallinity, and thermal stability of the polyesters are also discussed. The polyesters have decomposition temperatures in the range 372–438°C.     

Facile reduction of aromatic nitro/azido functionality on solid support employing Al/NiCl2·6H2O and Al/NH4Cl: synthesis of pyrrolo[2,1-c][1,4]benzodiazepines

An efficient and mild method for the reduction of aromatic nitro and azido groups on solid support using Al/NiCl₂·6H₂O and Al/NH₄Cl is described. This solid phase reduction technique has been applied towards the synthesis of DNA binding pyrrolo[2,1-c][1,4]benzodiazepine antitumour antibiotics.     

2‐Pyrazolines from 1,3 ‐ dipolar cycloaddition of diazomethane to arylsulfonylethenes

Novel 2‐pyrazolines were obtained by the cycloaddition of diazomethane to bis(arylsulfonylethenyl)‐sulfones ( 3 ) and 1‐arylsulfonyl‐2‐styrylsulfonylethenes (7). Dehydrogenation of 2‐pyrazolines with chloranil gave pyrazoles.     

Carbonyl and hydridocarbonyl complexes of ruthenium (II) and osmium (II) with tertiary arsines

Ruthenium halides (Cl and Br) react with monotertiary arsines-Ph₂RAs (R=Me, Et, Pr ⁿ ) in methoxyethanol, in the presence of aq. formaldehyde to give monocarbonyl complexes of ruthenium(II) of the type RuX₂(CO) (Ph₂RAs)₃. Carbonylation of an ethanolic solution containing ruthenium trichloride and the arsine at room temperature yieldtrans dicarbonyl compounds of the formula RuCl₂(CO)₂ (Ph₂RAs)₂. The osmium monocarbonyls OsX₂(CO) (Ph₂RAs)₃ (X=Cl, Br; R=Me, Et) react with NaBH₄ in methanol to yield complexes of the composition OsHX(CO) (Ph₂RAs)₃. The ruthenium analogues RuHCl(CO) (Ph₂RAs)₃ have also been made. Structures have been assigned to all these compounds on the basis of IR and NMR spectral results.     

Synthesis of tetrahydrofurans via silicon promoted Pummerer type reaction

A novel, unprecedented transformation of δ-hydroxysulfoxides into substituted tetrahydrofurans by a silicon promoted Pummerer type reaction is disclosed. The transformation is shown to be general and is brought about under very mild reaction conditions. The products with the sulfide group at the anomeric carbon provide a suitable handle to carry out further transformations.