N-Fluorobenzenesulfonimide [(PhSO₂)₂NF] - A Neutral N-F-Containing Electrophilic Fluorinating Agent

Biographical Sketches

Amin Rostami was born in Kurdistan/Divandareh, Iran in 1976. He received his M.Sc. in organic chemistry at Razi University in 2002. He is currently working for his Ph.D. in organic chemistry under the supervision of Professor Ardeshir Khazaei at both Bu-Ali Sina University^a and University of Kurdistan.^b His present research is focused on new applications of N-halo reagents in organic synthesis.

Introduction

N-Fluorobenzenesulfonimide [NFSI] is a stable crystalline solid that easy to handle, non-hygroscopic, soluble in most common ethereal and chlorinated solvents, and commercially available. It is a neutral N-F-containing electrophilic fluorinating agent that permits the incorporation of fluorine into neutral and carbanionic nucleophiles ranging from very reactive organometallic species to slightly activated aromatic compounds. [1]

N-Fluorobenzenesulfonimide can be employed in the preparation of aryl (difluoromethylenephosphonates), [2] 20-deoxy-20-fluorocamptothecin, [3] N-fluoro sulfon­amides, [4] 2-amino-5-fluorothiazole hydrochloride [5] and benzylic α,α-difluoronitriles, -tetrazoles, and -sulfonates. [6] When NFSI was associated with chiral palladium complexes an efficient method to catalytic enantioselective fluorination of β-keto esters, [7] and α-cyano acetates [8] was presented.

Abstracts

The use of imidazolidinone 1 as the asymmetric catalyst has been found to mediate the fluorination of aldehyde substrates with N-fluorobenzenesulfonimide serving as the electrophilic source of fluorine. A wide range of functional groups, including olefins, ­esters, amines, carbamates, and aryl rings, can be readily tolerated on the aldehydic substrate. [9]
Various N-alkylimines derived from acetophenones were successfully monofluorinated using N-fluorosulfonimide (NFSI) in a mixture of acetonitrile and DMF at 0 °C. Alternatively the same procedure without DMF gave rise to diflourinated imines when performed at room temperature. The obtained α- and α,α-difluorinated imines were subsequently reduced to give the corresponding β-fluoro- and β ,β-difluoroamines in good yield. [10]
NFSI was used for synthesis of novel 3,5-difluoropyridine-4-carb­oxaldehyde. Difluorination was achieved through the reaction of 3,5-dibromo-1,3-dioxolane pyridine with n-butyllithium followed by N-fluorobenzenesulfonimide at -120 °C in good yield. [11]
Reaction of the in situ generated purine C-8 carbanion of a pro­tected 5′-noraristeromycin derivative with N-fluorobenzenesulfon­imide gave 8-phenylsulfonyl-5′-noraristeromycin rather than the expected 8-fluoro derivative. A single electron transfer (SET) mechanism is proposed for this occurrence. The phenylsulfonyl product offers a structural feature common to some anti-HIV agents. [12]
α-Fluorosulfonamides were prepared by electrophilic fluorination of tertiary sulfonamides using N-fluorobenzenesulfonimide as fluorinating agent and utilizing the dimethoxybenzyl group (DMB) as a new sulfonamide protecting group. Removal of the DMB group with TFA/CH2Cl2 gave primary and secondary α-fluorosulfonamides. [13]
D. Y. Kim and coworkers reported the catalytic enantioselective fluorination of β-keto phosphonates catalyzed by a chiral palla­dium complex. Treatment of β -keto phosphonates with N-fluorobenzenesulfonimide (NFSI) as electrophilic fluorinating reagent under mild reaction conditions afforded the corresponding α-fluorinated β-keto phosphonates in moderate to excellent yields with excellent enantiomeric excesses. [14]

References

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