One-Pot Conversion of N-Arylglycines to Sydnones Efficiently Promoted by Bis-chlorine-1,4-diazabicyclo[2.2.2]octane Complex (Cl2-DABCO) in the Presence of NaNO2/Ac2O under Neutral Conditions

Synthesis of 2H-Indazoles by the [3 + 2] Dipolar Cycloaddition of Sydnones with Arynes

“…Sydnones are readily prepared from the corresponding amino acids 12 by a sequence which involves N -nitrosation/cyclodehydration. Three different protocols, namely Protocol 1A [1.5 equiv of NaNO 2 , 0 °C, 1 h, then acidify], Protocol 1B [2.0 equiv of NaNO 2 , HCl, then 0 °C, 1 h], and Protocol 1C [1.5 equiv of i -amyl nitrite, DME, rt, 2 d] have been used in the nitrosation step, and two other protocols, namely 2A [Ac 2 O as solvent, 110 °C, 2 h] and 2B [2 equiv of TFAA, Et 2 O, rt, 2 h] have been used for the cyclodehydration step.…”

“…The precipitate was filtered, washed thoroughly with cold water (slightly acidified by HCl to pH ∼4) and dried under a high vacuum to yield 2.6 g of crude N -(4-chlorophenyl)leucine as a slightly green solid (yield >100%). 12f,g It should be noted that this method did not work for Met or Thr. This crude amino acid was used in the next step without further purification.…”

Click and Bio-Orthogonal Reactions with Mesoionic Compounds

“…46 Finally, one-pot strategies were developed, avoiding the isolation of the toxic nitroso-amine intermediate. 47,48 In 2019, an alternative method using mechanochemistry was developed by the group of Lamaty. 49 Interestingly, the sydnone core offers various postfunctionalization possibilities, which have been the topic of several works, including reviews (Scheme 6b).…”

“…The nitrosylation step was also improved by Turnbull by using isoamyl nitrite, a milder reagent which requires only evaporation as workup . Finally, one-pot strategies were developed, avoiding the isolation of the toxic nitroso-amine intermediate. , In 2019, an alternative method using mechano-chemistry was developed by the group of Lamaty . Interestingly, the sydnone core offers various postfunctionalization possibilities, which have been the topic of several works, including reviews (Scheme b). ,− Indeed, the proton in position C 4 possesses an acidic character and can be abstracted in the presence of different organometallic species.…”

Synthesis of 2H-Indazoles by the [3 + 2] Cycloaddition of Arynes and Sydnones

“…The preparation of sydnones is readily achieved according to literature procedures, albeit in variable yields. The most easily accessed sydnone, N -phenylsydnone ( 2a ), has first been investigated as a representative substrate to test the feasibility of the reaction (Table ).…”