Direct Substitution of Hydroxy Group of π-Activated Alcohols with Electron-Deficient Amines Using Re₂O₇ Catalyst

Abstract

The first example of simple Re(2)O(7)-catalyzed direct dehydrative coupling between allylic alcohols with electron-deficient amines has been achieved under mild and open flask conditions. The protocol has also been successfully applied to benzylic and propargylic alcohols. The mechanistic proof for the S(N)1-type process has also been provided.

Mechanistic Insights into the Rhenium‐Catalyzed Alcohol‐To‐Olefin Dehydration Reaction

“…The mechanisms proposed in literature for the γ‐alumina‐catalyzed dehydration reaction, proceeding through an E2‐type mechanism,22–24 can be ruled out for the rhenium‐catalyzed reaction on the basis of the high activation energies found for the concerted mechanism, depicted in Figure 6. The mechanism presented here does resembles the one found for tungsten‐based polyoxometallates, for which also an E1‐type mechanism has been proposed,25 as well as the mechanism proposed for the dehydrative coupling of allylic alcohols using Re 2 O 7 , for which an S N 1 mechanism is proposed 27. As MTO and tungsten‐based polyoxometallates are based on neighboring third‐row transition metals, and both are in high oxidation states, primarily ligated by oxygen atoms, the similarity in mechanism is not unexpected.…”

“…For the various rhenium‐catalyzed reactions involving alcohols, including dehydration,9, 26 dehydrative coupling,27 etherification,9, 28 and 1,3‐transposition,29 different reaction mechanisms have been proposed in the literature. In most proposed mechanisms, the first step involves the reaction of MTO with the alcohol to form a [ReO 2 (Me)(OH)(OR)] intermediate.…”

Lewis‐Acid‐Catalyzed Intramolecular Aza‐Friedel–Crafts Reaction of N‐tert‐Butanesulfinyl Imines: Efficient Synthesis of Optically Active 9‐Aminofluorene Derivatives

“…However, the synthetic approaches to access these valuable compounds have received considerably less attention to date; only examples dealing with racemic intramolecular Friedel–Crafts alkylation,3a,b addition of imines,3c benzylic arylation,3d,e intermolecular amination of the CH bond,3f,g or cross‐coupling of the CN bond3h,i have been described. To the best of our knowledge, despite the potential importance of their related optically active compounds (Scheme , compound C ), the stereoselective construction of 9‐aminofluorene derivatives is even more underexplored, with only one report that touched upon attempts at asymmetric synthesis 3k.…”

Silicon‐Directed Rhenium‐Catalyzed Allylic Carbaminations and Oxidative Fragmentations of γ‐Silyl Allylic Alcohols

“…Re 2 O 7 is the least expensive and most widely available rhenium source and is significantly less costly than many Ru, Rh, Ir, Pt, and Pd catalysts 15. Ghorai demonstrated the use of Re 2 O 7 as a catalyst for the carbamination and amidation of 1,3‐disubstituted allylic alcohols including one example of an unsymmetrical substrate 14a. This single example provided the conjugated product as a single isomer [Eq.…”