Samarium diiodide reductive cleavage

J. L. Chiara, C. Destable, P. Gallego, and J. Marco-Contelles, Cleavage of N—O bonds promoted by samarium diiodide Reduction of free or N-acylated O-alkylhydroxylamines, /. Org. Chem., 61 (1996) 359-360. 

Sc(OTf)3 (4 mol%)-catalyzed addition of 1-trimethylsilyl nitropropanate to aryl and alkylimines was described [109]. The use of N-(4-methoxyphenyl)imines gave superior yields and/or diastereoselectivities of P-nitro amines in most cases (72-99% yield, antijsyn = 5/3-9/1). The products could be reduced to 1,2-diamines by samarium diiodide reduction, formation of the cyclic urea and cleavage of the 4-methoxyphenyl group with ceric ammonium nitrate (CAN). This methodology was later employed for the synthesis of pseudo-C2-symmetric triamines as candidates for human immunodeficiency virus (HIV) protease inhibition [110]. 

Burk et al. showed the enantioselective hydrogenation of a broad range of N-acylhydrazones 146 to occur readily with [Et-DuPhos Rh(COD)]OTf [14]. The reaction was found to be extremely chemoselective, with little or no reduction of alkenes, alkynes, ketones, aldehydes, esters, nitriles, imines, carbon-halogen, or nitro groups occurring. Excellent enantioselectivities were achieved (88-97% ee) at reasonable rates (TOF up to 500 h ) under very mild conditions (4 bar H2, 20°C). The products from these reactions could be easily converted into chiral amines or a-amino acids by cleavage of the N-N bond with samarium diiodide. 

Epoxy-l-haloalkenes undergo novel reductive cleavage reactions with samarium diiodide to give cyclopropanols or allylic alcohols depending upon the substrates and reaction conditions. Formation of the cyclopropanol is believed to proceed through a diradical intermediate <1998SL1073>. 

Reductive deamination of pyrrolidine (3) with samarium diiodide in THF-HMPA in the presence of methanol as the proton source yielded the desired piperidone (4) stereoselectively in 90% yield (Eq. (2)), where a carbon-nitrogen bond cleavage reaction and subsequent recyclization took place simultaneously (05TL5161). 

The reduction of benzo-fused bicyclic sulfonium ions with samarium diiodide also results in the cleavage of the —C bonds. However, as shown in Scheme 9, the regioselectivity here depends on... 

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