[21272-85-5] · C7H7NO4S · Phenylsulfonylnitromethane · (MW 201.22)
Physical Data: mp 78-79 °C; pK
Solubility: insol water; sol CH2Cl2, hot alcohol. Sodium salt (1) sparingly sol DMSO but not THF; lithium salt (2) sol THF.
Form Supplied in: white crystalline solid.
Analysis of Reagent Purity: analytical TLC (CH2Cl2 elution) should give one spot, R
Preparative Methods: Nitromethane, Sodium Benzenesulfinate, and Iodine are added sequentially to a cold (0-5 °C) DMF solution of Sodium Methoxide. The reagent can be converted to NaO2N=CHSO2Ph (1) and LiO2N=CHSO2Ph (2) using NaOMe and LiOMe, respectively.1
Handling, Storage, and Precautions: indefinitely stable; the nitronate salts (1) and (2) can be stored dry without decomposition for several weeks but, like all nitronate salts, they are explosive: (
The reagent can be C-monoalkylated via its nitronate salts (1) and (2). a-Nitro sulfones were obtained by reaction of (1) with a variety of benzyl halides and primary alkyl iodides (eq 1).1,4 a-Nitro sulfones were similarly obtained by reaction of (2) with allylic acetates in the presence of Pd0 catalysts (eqs 2 and 3).1,5 High regioselectivity for the less hindered carbon of the p-allylpalladium intermediate was typically observed. Displacement of the acetate usually occurs with net retention.6
C,C-Dialkylates were not formed in the alkylation reactions owing to congestion at the monoalkylated a-nitro sulfone center. However, internal O-alkylation can occur,1,7 subsequent to C-alkylation, affording cyclic nitronic esters (eq 4) which can be deoxygenated to provide 3-phenylsulfonyl-4,5-dihydroisoxazoles. The reagent has also been used to prepare a-nitro sulfones by Michael addition to 3-buten-2-one.4a a-Nitro sulfones can be converted to carboxylic acids,1,5 desulfonated nitro compounds,1,4a,8 and nitriles.1
The reagent is used to make three precursors for generation of the 1,3-dipole benzenesulfonyl cyanide N-oxide (PhSO2C&tbond;
However, nitronic ester (4), which has been known to explode, is a more easily obtained precursor: the reagent is simply methylated using diazomethane.2b,10 The reagent also reacts with nitric acid to provide bis(phenylsulfonyl)furazan 2-oxide (5), which is a third nitrile oxide precursor.9,2c
Any of these precursors, for example (3), can be used to generate the nitrile oxide which then reacts in situ with a wide variety of alkenes to give 3-phenylsulfonyl-4,5-dihydroisoxazoles (eq 6).2,10,11
The alkene configuration is retained in the dihydroisoxazole and regioselectivity is high for monosubstituted, gem-disubstituted, and trisubstituted alkenes. Conditions for generation of the nitrile oxide vary: (3) requires mild base2a or Silver(I) Nitrate,2b while nitronic ester (4) requires strong base2b or strong acid,12 and (5) requires heating (140 °C).2c The phenylsulfonyl group of the dihydroisoxazoles can be replaced using a variety of nucleophiles including organolithium reagents and sodium methoxide.13,7 Reductive cleavage using 2% Sodium Amalgam14 or Hexacarbonylmolybdenum7 affords cis-b-hydroxynitriles, and this is the most general route to these compounds (eq 7).
Peter A. Wade
Drexel University, Philadelphia, PA, USA