Kenneth Turnbull

The sydnone ring as an ortho-director of lithiation. Dilithiation of 3-phenylsydnone and trapping by electrophiles

Abstract Readily available 3-phenylsydnone ( 3 ) reacts with n -butyllithium/TMEDA to form the dilithio species 4 which can be trapped with suitable electrophiles. This represents the first use of a mesoionic ring system for directed lithiation.

Acylation of Sydnones with Acetic Anhydride in the Presence of Montmorillonite K-10

Abstract Various 4-acetyl sydnones 2 can be prepared in good yield by reaction of the corresponding 3-arylsydnones (cf. 1) with acetic anhydride at ∼ 110°C catalyzed by Montmorillonite K-10. The reaction fails where an ortho-keto moiety is present; therein sydnone ring cleavage occurs to form the corresponding indazole 3.

Debromination of 4-Bromo-3-arylsydnones with Sodium Sulfite

Abstract 4-Bromo-3-arylsydnones 1 are denominated to the corresponding 3-arylsydnones 2 in good to excellent yield using sodium sulfite in methanol/water. In contrast to previously employed reagents, the reduction is successful in the presence of electron-donating, electron- withdrawing and bulky groups.

Selectivity of 1,3-dipolar cycloaddition of methyl propiolate to 3-phenylsydnone in near- or supercritical carbon dioxide

Abstract The selectivity of the 1,3-dipolar cycloaddition reaction of methyl propiolate to 3-phenylsydnone was measured under various conditions of pressure (7.6–30.4 MPa) and temperature (333–423 K) in near- or supercritical carbon dioxide. The reaction produces a mixture of two regioisomers, 3-carbomethoxy-1-phenylpyrazole (isomer A) and 4-carbomethoxy-1-phenylpyrazole (isomer B). Reaction composition was measured by high-performance liquid chromatography (HPLC). A supercritical fluid extraction (SFE) instrument, programmed in the static mode, was used as the reaction apparatus. The selectivity (isomer A/isomer B) of the reaction was compared with the selectivity in toluene at 353 K. For both solvents, selectivity did not vary over time for up to 12 h in CO2 and 67 h in toluene. The mean selectivity measured in toluene was 3.62 compared with 5.08 in CO2. At 7.6 MPa and 1 h in CO2, the selectivity decreased with increasing temperature from 5.52 at 353 K to 3.14 at 423 K. At 353 K and 3 h, the selectivity increased with increasing pressure from 4.96 at 7.6 MPa to 6.56 at 30.4 MPa, however, the yield decreased by 50%. Overall, lower pressure and higher temperature gave higher yields while higher pressure and lower temperature produced greater selectivity of isomer A over isomer B.

Reduction of Aroyl Azides with Sodium Borohydride/Nickel (II) Chloride

Abstract Aroyl azides (cf. 1) generally are reduced to the corresponding amides 2 in very high yield and under mild conditions using the sodium borohydride / nickel (II) chloride system.

Formation of 1-bromocarbonylindazoles via cleavage of 4-bromo ortho-substituted arylsydnones with HBr

Abstract Treatment of 4-bromo-3-arylsydnones containing an ortho -carbonyl substituent ( cf . 1d-j ) with HBr gas leads to the corresponding, novel 1-bromocarbonyl-3-substituted indazoles ( 2d-k ), generally in excellent yield.

Bismuth Triflate–Catalyzed Friedel–Crafts Acylations of Sydnones

Abstract Friedel–Crafts acylations of various 3-arylsydnones at the C4 position have been achieved in good yields using 4 equivalents of an alkyl anhydride and 25 mol% each of bismuth triflate and lithium perchlorate in anhydrous acetonitrile at 95 °C. Acylations appear to be faster with arylsydnones bearing electron-donating moieties and sterically unencumbered anhydrides. GRAPHICAL ABSTRACT

Direct Carboxamidation of Sydnones with Chlorosulfonyl Isocyanate

Abstract Various 4-carboxamido sydnones 2 can be prepared in good yield by reaction of the corresponding 3-substituted sydnones (cf. 1) with chlorosulfonyl isocyanate at room temperature.

The reaction of 4-substituted aroyl azides with NaBH4TFA

Treatment of 4-substituted aroyl azides (cf.1a-e) with NaBH4TFA leads to the corresponding, novel 4-substituted N,N-di(2,2,2-trifluoroethyl)aniline derivatives (2a-e) in excellent yield except where electron-withdrawing groups are present (cf.1f-g).

CHLORINATION OF 3-SUBSTITUTED SYDNONES WITH DICHLOROIODOBENZENE

Abstract 3-Substituted sydnones (cf. 1) form the 4-chloro congeners 3 cleanly, in good yield using PhICl2 in the presence of triethylamine.