[118922-13-7] · C15H13NO2S · (E,E)-N-Phenylsulfonyl-4-phenyl-1-aza-1,3-butadiene · (MW 271.36)
(electron-deficient acyclic 1-azadiene capable of participation in inverse electron demand Diels-Alder reactions with electron-rich dienophiles2a)
Alternate Name: (E,E)-N-(3-phenyl-2-propenylidene)benzenesulfonamide.
Physical Data: mp 107-109 °C.
Solubility: sol CH2Cl2, C6H6.
Form Supplied in: pale yellow solid.
Preparative Methods: a solution of cinnamaldehyde in toluene (0.10 M) is treated with benzenesulfonamide (1.1 equiv) and MgSO4 (2 g mmol-1) and the reaction mixture is stirred at reflux for 120 h. The reaction mixture is cooled to 25 °C, the MgSO4 is removed by filtration, and the filtrate is concentrated in vacuo. Flash chromatography (SiO2, 15% EtOAc/hexane eluent) gives the title reagent (typical yield 50%).2
Additional general methods for the synthesis of N-sulfonylimines based on the in situ generation of O-sulfinate derivatives of oximes employing sulfinyl chlorides (phenyl- and methylsulfinyl chloride)2a,3-8 or sulfonyl cyanides (p-toluenesulfonyl cyanide)2b and their subsequent rt rearrangement have been detailed.
Handling, Storage, and Precautions: stable at room temperature but susceptible to hydrolysis and must be stored free of moisture.
Stable, electron-deficient N-(phenylsulfonyl)-1-aza-1,3-butadiene is one of a series of a,b-unsaturated N-benzenesulfonyl imines capable of participation in regio- and endo-selective inverse electron demand Diels-Alder reactions with a range of electron-rich dienophiles employed in the diastereoselective preparation of substituted N-benzenesulfonyl-1,2,3,4-tetrahydropyridines (eq 1).2a,3
N-Benzenesulfonyl aldimines have been shown to be more reactive than N-benzenesulfonyl ketimines (eq 2),1,2a,3 and the complementary addition of a C-3 or the noncomplementary addition of C-2 and C-4 electron-withdrawing substituents substantially accelerate the Diels-Alder reaction and maintain the expected cycloaddition regioselectivity and exceptionally high endo diastereoselectivity (eqs 3-5).2a,3-5
Synthetic procedures for preparation of highly substituted or highly functionalized pyridines based on the [4 + 2] cycloaddition reactions of N-sulfonyl-1-aza-1,3-butadienes have been developed and their applications in the total syntheses of fredericamycin A (2) (eq 6)6 and streptonigrone (3) (eq 7)7 have been described. The intramolecular [4 + 2] cycloaddition reactions of N-sulfonyl-1-aza-1,3-butadienes have been detailed.8
Dale L. Boger & Minsheng Zhang
The Scripps Research Institute, La Jolla, CA, USA