Reduction of sulfoxides and pyridine-N-oxides over iron powder with water as hydrogen source promoted by carbon dioxide

Abstract

A green process was developed for efficient reduction of sulfoxides and pyridine-N-oxides using the iron powder in the presence of H 2 O-CO 2 to sulfides and pyridines, respectively. Notably, H 2 O is employed as the terminal hydrogen source, and CO 2 could enhance hydrogen generation through in situ formation of carbonic acid. Thus carbonic acid offers simple neutralization by depressurizing CO 2 and the system can eliminate unwanted byproducts. The high generality and chemo-selectivity of this protocol were demonstrated by the scope of substrates, in which chlorine, vinyl group and benzene ring can be tolerated.

I2/K2S2O8: An Unprecedented Deoxygenating System for N‐Oxides and Sulfoxides

“…Other reagents such as sulfur reagents, phosphorus reagents, were also used for deoxygenation. On other side, different catalytic systems have been employed for the deoxygenation of sulfoxide viz., B(C 6 F 5 ) 3 /hydrosilanes, I 2 , Zn(OTf) 2 /boranes, ruthenium nanoparticles, silane/MoO 2 Cl 2 , oxo complexes, gold nanoparticles, SOCl 2 , and Fe powder, etc.…”

Efficient Chemoselective Reduction of N‐Oxides and Sulfoxides Using a Carbon‐Supported Molybdenum‐Dioxo Catalyst and Alcohol

“…In previous reports of N ‐oxide reduction, particularly those using strong reducing agents, concurrent reduction of sulfoxide moieties is frequently observed, such as with PhSiH 3 /MoO 2 Cl 2 , H 2 /MoO 2 Cl 2 , and the Fe/CO 2 /H 2 O system reported by the Romao, Royo, and He groups respectively . Given the chemo‐selective nature of our catalyst described above, we were intrigued to explore whether the heterogeneous Mo@C system can differentiate between N ‐oxide and sulfoxide reduction within the same reaction flask (Scheme ).…”

“…[3] In previous reports of N-oxide reduction, particularly those using strong reducing agents, concurrent reduction of sulfoxide moieties is frequently observed, such as with PhSiH 3 /MoO 2 Cl 2 , H 2 /MoO 2 Cl 2 , and the Fe/CO 2 /H 2 O system reported by the Romao, Royo, and He groups respectively. [14,17,34] Given the chemo-selective nature of our catalyst described above, we were intrigued to explore whether the heterogeneous Mo@C system can differentiate between N-oxide and sulfoxide reduction within the same reaction flask (Scheme 3). Interestingly, when a one pot competition reaction between pyridine N-oxide and methyl phenyl sulfoxide is conducted using a slight excess of benzyl alcohol, monitoring of the reaction mixture shows that the sulfoxide remains intact until complete conversion of pyridine N-oxide is achieved.…”

B(C6F5)3‐Catalyzed Deoxygenation of Sulfoxides and Amine N‐Oxides with Hydrosilanes

“…[5] The past decade has witnessed spectacular advances in metal-free catalytic reductions, particularly with the use of B(C 6 F 5 ) 3 /silanes. Over the past years, many systems have been employed for the deoxygenation of sulfoxides, including reagents such as silane/MoO 2 Cl 2 , [6] oxo complexes, [7] gold nanoparticles, [8] zinc(II) trifluoromethanesulfonate/bis(pinacolato)diboron [Zn(OTf ) 2 /B 2 (pin) 2 ] or Zn(OTf ) 2 /boranes, [9] SOCl 2 , [10] Fe powder, [11] ruthenium nanoparticles, [12] and I 2 . Over the past years, many systems have been employed for the deoxygenation of sulfoxides, including reagents such as silane/MoO 2 Cl 2 , [6] oxo complexes, [7] gold nanoparticles, [8] zinc(II) trifluoromethanesulfonate/bis(pinacolato)diboron [Zn(OTf ) 2 /B 2 (pin) 2 ] or Zn(OTf ) 2 /boranes, [9] SOCl 2 , [10] Fe powder, [11] ruthenium nanoparticles, [12] and I 2 .…”

“…Consequently, the combined use of B(C 6 F 5 ) 3 and hydrosilanes allows the deoxygenation of alcohols [3] and ethers [4] as well as carbonyl compounds and their derivatives. Over the past years, many systems have been employed for the deoxygenation of sulfoxides, including reagents such as silane/MoO 2 Cl 2 , [6] oxo complexes, [7] gold nanoparticles, [8] zinc(II) trifluoromethanesulfonate/bis(pinacolato)diboron [Zn(OTf ) 2 /B 2 (pin) 2 ] or Zn(OTf ) 2 /boranes, [9] SOCl 2 , [10] Fe powder, [11] ruthenium nanoparticles, [12] and I 2 . [2] In addition, the reduction of sulfoxides and amine N-oxides into their corresponding sulfides and amines is an important reaction owing to its considerable utility in organic synthesis.…”