Carlo Dell'Erba

A mild and efficient SRN1 approach to diaryl sulfides from arenediazonium tetrafluoroborates

Abstract The reaction between arenediazonium tetrafluoroborates and sodium arenethlolates in Me2SO at 25°C represents an efficient access to diaryl sulfides. A number of evidences suggest the occurrence of a radical, radical-anion SRNl mechanism, the arenethlolate acting both as electron donor and as aryl-radical trapping nucleophile. Valuable improvements with respect to recent SRNl syntheses of diaryl sulfides from haloarenes are represented. Inter alia , by the compatibility of both electron-withdrawing and releasing substituents as well as by the insensitivity to steric hindrance In the diazonlum salt. When the arenedlazonlum ion bears another SRNl leaving group (such as Cl, Br, or I) disubstitution products are predomnantly formed.

Synthetic exploitation of the ring-opening of 3,4-dinitrothiophene. Access to 1,4-disubstituted 2,3-dinitro-1,3-butadienes and 2,3-butanedione dioximes

Abstract The reactions of 1,4-bis(diethylamino)-2,3-dinitro-1,3-butadiene 1 (deriving from ring-opening of 3,4-dinitrothiophene with diethylamine) with one mole of Grignard reagents give, together with disubstituted products 1,4-dialkyl- and 1,4-diaryl-2,3-dinitro-1,3-butadienes 2, the monosubstituted 1-alkyl-4-diethylamino- and 1-aryl-4-diethyl-amino-2,3-dinitro-1,3-butadienes 8 in yields dependent on the nature of the reagent employed. Aryl-substituted compounds 8 undergo a highly regioselective reaction with aryl Grignard reagents to furnish good yields of 1-Ar1-4-Ar2-2,3-dinitro-1,3-butadienes 9. Preliminary results are also reported on the transformation of some dinitrobutadienes 2 and 9 into the corresponding 1,4-disubstituted 2,3-diaminobutanes 10.

Synthetic exploitation of the ring-opening of 3,4-dinitrothiophene. A novel access to 1,4-dialkyl- and 1,4-diaryl-2,3-dinitro- 1,3-butadienes

Abstract (E,E)-1,4-Bis(diethylamino)-2,3-dinitro-1,3-butadiene ( 2a ), obtained from the ring-opening of 3,4-dinitrothiophene, reacts with Grignard reagents in THF to give good yields of 1,4-disubstituted ( Et, cy-Hex, Ph ) 2,3-dinitro- 1, 3-butadienes ( 3a –c) having almost exclusively (E,E) configuration.

Ring opening of 2-substituted 4-nitrothiophenes with pyrrolidine. Access to new functionalized nitro-unsaturated building blocks

Abstract The reaction conditions of the ring-opening processes of 3-nitrothiophene 7a and of 3-nitrobenzo[b]thiophene 7b with pyrrolidine and silver nitrate were optimized as well as those of the subsequent S-methylation of the ensuing silver enethiolates 8a and 8b to 4-methylthio-2-nitro-1-pyrrolidino-1,3-butadiene 9a and 1-(2-methylthiophenyl)-1-nitro-2-pyrrolidinoethylene 9b. Under such conditions 2-X-substituted 4-nitrothiophenes 7c–i consistently gave good yields of the corresponding 4-methylthio-2-nitro-1-pyrrolidino-4-X-1,3-butadienes 9c–i. The nitroenamine derivatives 9a–i were then reacted with p-tolylmagnesium bromide to furnish moderate to good yields of 4-methylthio-2-nitro-1-(p-tolyl)-4-X-1,3-butadienes 10a,c–i and 1-(2-methylthiophenyl)-1-nitro-2-(p-tolyl)ethylene 10b. Stereochemistry of the interesting building blocks 9a–i and 10a–i was assigned on the grounds of 1H NMR data and NOE experiments.

A convenient srn1 synthesis of aromatic nitriles from diazonium salts via diazosulfides

Properly substituted diazosulfides XC6H4-N=N-SPh (1) (either isolated or generated in situ from arenediazonium tetrafluoroborates and sodium benzenethiolate) react with tetrabutylammonium cyanide, in Me2SO under photon or electron stimulation, leading to nitriles XC6H4CN (2). Satisfactory yields of 2, comparable with those of the Sandmeyer reaction, are obtained when X = 3- or 4-CF3 , 2-, 3-, or 4-CN, 4-F, 4-MeO, 3-MeCO, 4-NO2, 4-PhCO, and 4-PhSO2. For different reasons, the reaction practically fails as a useful nitrile synthesis when X = H, 4-MeO, 2-, or 3-NO2. The collected evidences agree well with the intervention of an SRN1 mechanism, to which diazosulfides 1, given their easy reduciblity followed by a prompt fragmentation of the C-N and N-S bonds, are convenient participating substrates. An important consequence of the mechanism involved is the behaviour of bromo and chloro derivatives (1: X = Br, Cl) which lead, through the contemporaneous introduction of two cyano functionalities, to more than satisfactory yields of the corresponding dicyanobenzenes.

A novel approach to 1H-indazoles via arylazosulfides

Abstract Treatment of variously substituted ( o -alkylaryl)azosulfides 1a-n with potassium tert -butoxide in DMSO at room temperature smoothly furnishes 1 H -indazoles 2a-n .

α-arylation vs. α-arylhydrazonylation of alkyl aryl ketones with arylazo tert-butyl sulfides

Abstract Potassium enolates of alkyl aryl ketones react selectively in DMSO with phenylazo 1a and 4 -methylphenylazo tert-butyl sulfide 1b undergoing respectively effective α-phenylation via S RN 1 and α-(4-methylphenyl)hydrazonylation via elimination-addition.

Arylation of potassium 2,4-pentanedionate via SRN1 on diazosulfides.

Abstract Potassium 2,4-pentanedionate reacts with diazosulfides (E)-1 and (Z)-2 in DMSO to give 3-aryl-2,4-pentanediones 3 via an S RN 1 process. Advantages and drawbacks of such new access to 3 are reported together with relevant mechanistic implications.

SRN1 C-arylation of phenols by azosulfides; A novel synthesis of dibenzo[b,d]pyran-6-ones

Abstract The ortho-arylation of phenols by (2-cyanoaryl)azo t-butyl (or phenyl) sulfides in SRN1 conditions, followed by a silica-gel-catalysed lactonisation of the resulting 2-cyano-2′-hydroxybiphenyls, leads to dibenzo[b,d]pyran-6-ones.

Base-induced cycloaddition of tosylmethyl or (tert-butoxycarbonyl)methyl isocyanide to 1,4-disubstituted 2,3-dinitro-1,3-butadienes. Access to 2,3-disubstituted 4-ethynylpyrroles

Abstract The reactions of 1,4-disubstituted 2,3-dinitro-1,3-butadienes 1a-g in THF with isocyanides XCH2NC (TosMIC, X = tosyl; TBICA, X = COOBut) and DBU furnish good to moderate yields of 2,3-disubstituted 4-ethynylpyrroles 5a-g or 6a-g. In the reaction of 1g with TosMIC and DBU the nitrovinyl pyrrole 7g and the 3,3′-dipyrrole 4g are also isolated as by-products. A mechanism involving sequential base-induced addition, elimination and cyclization steps is advanced to account for the formation of the isolated products.