Synthesis and Structure of Hypervalent Diacetoxybromobenzene and Aziridination of Olefins with Imino-λ3-bromane Generated in Situ under Metal-Free Conditions
摘要:
Ligand exchange of p-CF3C6H4BrF2 with acetoxy groups using AcOH and Ac2O affords (diacetoxybromo)benzene in a high yield, which undergoes azirldination of alkenes In the presence of TfNH2 and sulfamate esters in one pot under mild conditions. The azirldination with TfNH2 proceeds stereospecifically with retention of stereochemistry of olefins at room temperature using limiting amounts of olefins under transition-metal-free conditions. The one-pot aziridination procedure using sulfamate esters can be applied to the Intramolecular versions.
Exposure of sulfides and sulfoxides to trifluoromethanesulfonylimino(aryl)‐λ3‐bromane in dichloromethane at 0 °C results in a facile transfer of the sulfonylimino group to sulfur atoms and affords N‐triflylsulfilimines and ‐sulfoximines in high yields under transition‐metal‐free conditions. Imination of (R)‐methyl p‐tolyl sulfoxide proceeded with predominant retention of configuration at the stereogenic
We present the first synthesis of air/moisture-stable λ3-bromanes (9 and 10) by using a cyclic 1,2-benzbromoxol-3-one (BBX) strategy. X-ray crystallography and NMR and IR spectroscopy of N-triflylimino-λ3-bromane (12) revealed that the bromine(III) center is effectively stabilized by intramolecular R–Br–O hypervalent bonding. This strategy enables the synthesis of a variety of air-, moisture-, and
Sulfonylimino-λ3-bromane functions as a reactive nitrenoid, because of the hyperleaving group ability of aryl-λ3-bromanyl groups, and undergoes transimidations to iodobenzenes at room temperature under metal-free conditions probably via an SN2-type nitrenoid transition state, yielding sulfonylimino-λ3-iodanes.
Direct Transfer of the Sulfonylimino Group of Imino-λ<sup>3</sup>-Bromane to <i>N</i>-Heterocycles and Trialkylamines: Synthesis of <i>N</i>-Iminoammonium Ylides under Metal-Free Conditions
Exposure of N-heterocycles and aliphatic trialkylamines to trifluoromethanesulfonylimino-lambda(3)-bromane at room temperature results in direct transfer of the sulfonylimino group to the nitrogen atoms and affords a variety of iminoammonium ylides under transition-metal-free conditions. The imino-lambda(3)-bromane probably serves as an active nitrenoid species without any activation and produces the ammonium ylides via a bimolecular nucleophilic substitution process.
A New Type of Imido Group Donor: Synthesis and Characterization of Sulfonylimino-λ<sup>3</sup>-bromane that Acts as a Nitrenoid in the Aziridination of Olefins at Room Temperature under Metal-Free Conditions
A stable sulfonylimino-lambda(3)-bromane, CF3SO2N--Br+C6H4-p -CF3, has been syntesized and structurally characterized for the first time. X-ray crystallographic analyses indicated a centrosymmetric dimer structure with little double-bond character for the "ylidic" Br-N bond. THe iminobromane serves as an efficient imido group donor and directly u ndergoes aziridination of olefins stereospecifically of alkenes under transition-metal-free conditions. The observed rate constants for aziridination of cis -cyclooctene are proportional to concentration of the olefin. The results suggest the involvement of a bimolicular transition state, in which an olefin attacks the sigma(*) N-Br orbital of iminobromane in the nitrenoid transfer process.