[55962-05-5] · C13H12INO2S · [N-(p-Toluenesulfonyl)imino]phenyliodinane · (MW 373.23)
(nitrogen atom source; reacts with heteroatom lone pairs to form ylides; capable of C-H bond insertion or alkene aziridination in the presence of transition metal catalysts)
Physical Data: mp 102-104 °C (dec).1
Solubility: v sl sol nonpolar solvents; sol DMSO (decomposes slowly); reacts with THF, MeOH.
Form Supplied in: light yellow solid, commercially available.
Analysis of Reagent Purity: 1H NMR spectra can be obtained in DMSO-d6, although the reagent slowly reacts with the solvent. Other assays include iodometric analysis1 and reaction with triphenylphosphine to form the phosphinimine.2
Preparative Methods: prepared by the reaction of PhI(OAc)2 with TsNH2 and KOH in MeOH, from which the product precipitates upon addition of water (eq 1).1 Another preparation employs the reaction of TsNH2 with PhI(OMe)2 in MeOH or in CH2Cl2 (eq 2).2
Handling, Storage, and Precautions: store at -20 °C; should be used within 6 months. The reagent can be weighed out in air. No known toxicity. Use in a fume hood.
PhI=NTs reacts with heteroatom lone pairs to generate ylides.1 Reaction with Triphenylphosphine at 100 °C affords 69% of the phosphinimine (1) (eq 3). Likewise, PhI=NTs reacts with Thioanisole to generate the iminosulfurane (2) in 49% yield (eq 4) and with Dimethyl Sulfoxide to quantitatively produce the sulfoximine (3) (eq 5).
PhI=NTs can be employed as a nitrogen source in the transition metal-catalyzed amination of alkanes and the allylic amination of alkenes. Manganese porphyrin complexes catalyze the amination of cyclohexane to generate N-tosylcyclohexylamine in 15% yield, while adamantane is aminated in 56% yield (eqs 6 and 7).3 Manganese porphyrins also catalyze the amination of alkenes to generate allylic amine derivatives.4 In this manner, N-tosyl-2-cyclohexeneamine was synthesized in 70% yield based on oxidant (eq 8). The amination of open-chain alkenes is hampered by attenuated reactivity and poor regioselectivity.
A complex generated in situ by the addition of Iron(II) Chloride to Chloramine-T effects similar aminations of hydrocarbons.5 When adamantane is introduced to a solution of this complex, N-tosyladamantan-1-amine is isolated in 63% yield (eq 9). Extension of the reaction to other substrates is complicated by the generation of chlorine-containing products.
The insertion of nitrenes, generated via the photolysis or thermolysis of azides, into C-H bonds is well known, although the yields are generally poor.6,7 However, when Ethyl Azidoformate is thermolyzed in the presence of 1-chlorocyclohexene, the allylic insertion product is formed in 49% yield (eq 10).8 In this case it is not clear if the product is formed through direct insertion or by the ring opening of an aziridine intermediate.
Iron- and manganese-porphyrin complexes catalyze the reaction of PhI=NTs with alkenes to form the corresponding N-tosylaziridines.9 Mn(TPP)Cl is generally a better catalyst than the analogous iron complex, affording 80% of the aziridine from the reaction with styrene (eq 11). Good yields are also obtained in the manganese-catalyzed reactions with 1,1- and 1,2-diphenylethylenes.10 Yields of aziridines derived from aliphatic alkenes remain low and are complicated by the formation of allylic amines.
Copper-based complexes have been found to be excellent catalysts for the aziridination of alkenes employing PhI=NTs as the nitrene precursor (eq 12).11 Both CuI and CuII efficiently catalyze the reaction, and the best results are usually obtained with the cationic complexes Tetrakis(acetonitrile)copper(I) Perchlorate and Copper(II) Trifluoromethanesulfonate. Good yields are obtained with a variety of substrates, including aliphatic alkenes and enolsilanes (eq 13), the latter delivering a-amino ketones upon hydrolysis of the intervening silyloxyaziridine.
Other nitrene precursors have been employed in the aziridination of alkenes. Azides have been shown to form aziridines when photolyzed or thermolyzed in the presence of alkenes, though these reactions usually exhibit low yields.12,13 However, the possibility of a transition metal-catalyzed process remains. In 1968, it was reported that heating Benzenesulfonyl Azide with cyclohexene in the presence of Copper powder produces the corresponding aziridine, albeit in low yield (15%).14 Pd0 catalyzes the aziridination of allylic ethers with methyl azidoformate.15
The copper-catalyzed aziridination reaction can be rendered enantioselective by the addition of chiral ligands. The first example of an enantioselective aziridination of an alkene employed the bis(oxazoline) ligand (4) (R = t-Bu) and Copper(I) Trifluoromethanesulfonate as the metal catalyst (eq 14).16 This catalyst system affords the aziridine in 97% yield and 61% ee. Other reports have appeared subsequently regarding the extended scope of this reaction.17-21 Important contributions to this area include the copper/bis(oxazoline)-catalyzed aziridination of aryl acrylate esters (eq 15)20 and the copper/bis(imine)-catalyzed aziridination of cyclic cis-alkenes with the bis(imine) ligand (5) (eqs 16 and 17).19
The Pd-catalyzed reaction of PhI=NSO2Ar in the presence of CO generates the isocyanates ArSO2NCO.22 Thus Bis(benzonitrile)dichloropalladium(II) catalyzes the formation of the isocyanate TsNCO (which can be isolated as the urea (6) in 60% yield after reaction with 2-chloroaniline) with PhI=NTs (eq 18). This reaction has been reported for several arylsulfonylimino iodinanes. Similar results can be achieved, however, by employing the less expensive chloramine-T and its derivatives as reagents.23
David A. Evans & David M. Barnes
Harvard University, Cambridge, MA, USA