Highly Chemoselective Calcium‐Catalyzed Propargylic Deoxygenation

A calcium‐catalyzed direct reduction of propargylic alcohols and ethers has been accomplished by using triethylsilane as a nucleophilic hydride source. At room temperature a variety of secondary propargylic alcohols was deoxygenated to the corresponding hydrocarbons in excellent yields. Furthermore, for the first time, a catalytic deoxygenation of tertiary propargylic alcohols was generally applicable. The same protocol was suitable for an efficient reduction of secondary as well as tertiary propargylic methyl, benzyl and allyl ethers. Substrates containing an additional keto‐, ester or secondary hydroxyl function were reduced with exceptional chemoselectivity at the propargylic position.     

Deoxygenation of biomass-derived feedstocks: oxorhenium-catalyzed deoxydehydration of sugars and sugar alcohols

Turn sugar into oil: The deoxygenation reaction of sugar moieties is important for the conversion of biomass into chemicals and fuels. The methyltrioxorhenium-catalyzed deoxydehydration reaction was successfully applied to this purpose using another alcohol as solvent/reductant. The reaction was highly stereospecific, affording linear polyene products from C(4) -C(6) sugar alcohols and aromatic compounds from C(4) -C(6) sugars.     

Acid‐, Water‐ and High‐Temperature‐Stable Ruthenium Complexes for the Total Catalytic Deoxygenation of Glycerol to Propane

The ruthenium aqua complexes [Ru(H₂O)₂(bipy)₂](OTf)₂, [cis‐Ru(6,6′‐Cl₂‐bipy)₂(OH₂)₂](OTf)₂, [Ru(H₂O)₂(phen)₂](OTf)₂, [Ru(H₂O)₃(2,2′:6′,2′′‐terpy)](OTf)₂ and [Ru(H₂O)₃(Phterpy)](OTf)₂ (bipy=2,2′‐bipyridine; OTf^?=triflate; phen=phenanthroline; terpy= terpyridine; Phterpy=4′‐phenyl‐2,2′:6′,2′′‐terpyridine) are water‐ and acid‐stable catalysts for the hydrogenation of aldehydes and ketones in sulfolane solution. In the presence of HOS(O)₂CF₃ (triflic acid) as a dehydration co‐catalyst they directly convert 1,2‐hexanediol to n‐hexanol and hexane. The terpyridine complexes are stable and active as catalysts at temperatures ≥250 °C and in either aqueous sulfolane solution or pure water convert glycerol into n‐propanol and ultimately propane as the final reaction product in up to quantitative yield. For the terpy complexes the active catalyst is postulated to be a carbonyl species [(4′‐R‐2,2′:6′,2′′‐terpy)Ru(CO)(H₂O)₂](OTf)₂ (R=H, Ph) formed by the decarbonylation of aldehydes (hexanal for 1,2‐hexanediol and 3‐hydroxypropanal for glycerol) generated in the reaction mixture through acid‐catalyzed dehydration. The structure of the dimeric complex [{(4′‐phenyl‐2,2′:6′,2′′‐terpy)Ru(CO)}₂(μ‐OCH₃)₂](OTf)₂ has been determined by single crystal X‐ray crystallography (Space group P (a=8.2532(17); b=12.858(3); c=14.363(3) Å; α=64.38(3); β=77.26(3); γ = 87.12(3)°, R=4.36 %).     

Reductive Deoxygenation of Carbonyl to Methylene by LiAlH4／InBr3

The reductive deoxygenation of aldehydes and ketones into the corresponding alkanes is accomplished by LiAlH4 in the presence of Lewis acid InBr3. It provides a convenient method to complete the transformation from carbonyl compounds to alkanes.     

Entry into Major Groups Retaining Taxol via Sinenxan A

Compound 1 as a key intermediate of 1,7,9-trideoxytaxol was synthesized in ten steps from a biosynthetically available taxane,Sinenxan A. The key steps in the synthesis were deoxygenation at C-14,allylic oxidation at C-13 and construction of the oxetane ring.     

Synthesis of the tricyclic dihydrofuran moiety of azadirachtin: efficient transformation of the Claisen rearrangement intermediate into a functionalized tricyclic dihydrofuran core

Azadirachtin is a C-seco limonoid, derived from the neem tree. Previously, we reported the synthesis of the right and left segments of azadirachtin, in addition to the coupling reaction of the modeled ester utilizing Claisen rearrangement. Herein we report the transformation of the modeled rearrangement product into a tricyclic dihydrofuran, which would be expected to have bioactivity against insects.     

A new regioselective synthesis and ambient light photochemistry of quinazolin-1-oxides

Quinazolin-1-oxides were prepared by the oxidation of tetrahydroquinazolines with H₂O₂-tungstate and their ambient light photochemistry was investigated. Substituent effects on their photochemical cyclization and the reactions of the products 1aH-[1,2]oxazireno[2,3-a]quinazolines under photochemical and thermal conditions are reported. The cyclization of quinazolin-1-oxides and the reactions of 1aH-[1,2]oxazireno[2,3-a]quinazolines show pronounced solvent isotope and solvent effects.     

Ph_3P/Mo~Ⅵ体系对亚砜类的脱氧反应

亚砜是有机合成的重要中间体,但反应完成后,往往需要除去亚砜基团,通常的方法是将亚砜脱氧为硫醚,再用Raney镍等除去硫醚基团:     

碲氢化钠对α-二酮的部份还原及对RnXO(X=N,As,s;n=2,3)的脱氧

有机碲化学最近几年采发展很快,许多有机碲化合物都是有用的试剂。我们已相继报道了碲氢化钠对亚胺的还原反应。在碲氢化钠的存在下,可由羰基化合物和伯胺一步合成     

Reflections on the mechanism of the Barton-McCombie Deoxygenation and on its consequences2

The Barton-McCombie deoxygenation is a landmark reaction in organic chemistry. Its efficiency in generating carbon radicals from alcohols is unmatched, despite the passage of more than 40 years since its discovery. Its mechanism, far from being straightforward, is in fact quite subtle and conceptually part of a much larger family of very powerful thiocarbonyl controlled radical reactions. This general mechanistic manifold encompasses the degenerate transfer of xanthates and related thiocarbonylthio congeners, a process that also subtends the now popular RAFT/MADIX polymerization technology, the remarkably versatile Barton decarboxylation via thiohydroxamate esters, the generation of nitrogen-centered radicals from oxime xanthates and thiosemicarbazones and thiosemicarbazides, and certainly other transformations that will emerge in the coming years. The present overview retraces the history of the Barton-McCombie reaction, the evolution of the mechanistic aspects and the resulting consequences in terms of new transformations and synthetic applications.