Cu(BF4)2·xH2O: A versatile catalyst

Abstract

(A) Acylation reactions: Acetylation of structurally diverse phenols, alcohols, thiols, and amines with stoichiometric amounts of Ac2O under solvent-free conditions at room temperature has been efficiently catalyzed by Cu(BF4)2·xH2O. Excellent chemoselectivity was observed during reaction with secondary and tertiary alcohols without any competitive dehydration and no rearrangement took place with allylic and propargylic substrates. (Chemical equation presented) (B) Diacetate formation: A strong catalytic effect of Cu(BF4) 2·xH2O has also been observed in the formation of aldehyde 1,1-diacetates from aldehydes and acetic anhydride under solvent-free conditions at room temperature. The rate of reaction was found to be very fast and in most of the cases the reaction was completed in 1-20 minutes in excellent yields, which could make this method more attractive and industrially viable. (Chemical equation presented) (C) Conjugate addition: Cu(BF4) 2·xH2O has been found to be a new and highly efficient catalyst for Michael addition of thiols to α,β-unsaturated carbonyl compounds under msolvent-free conditions. (Diagram presented) (D) Electrophilic ring opening: A ring opening of siloxycyclopropane, via β-copper substituted ketone intermediate, is efficiently catalyzed by Cu(BF4)2·xH2O leading to the formation of a 1,6-diketone. The reaction takes place in 0.5-1 hour at 15 °C in Et2O. (Diagram presented) (E) Epoxide ring opening by alcohols: A general, simple and efficient protocol has been developed for ring opening of different epoxides by reaction with various alcohols under the catalytic influence of Cu(BF4)2·xH2O. The reactions were carried out at room temperature and offered the use of cheap and commercially available copper tetrafluoroborate. (Diagram presented) (F) Epoxide ring opening by amines: Another mild, efficient and selective ring opening of epoxides has been effected by amines leading to the synthesis of β-amino alcohols under the catalytic effect of Cu(BF4)2· xH2O. The mild reaction conditions, short reaction times, solvent-free conditions, and excellent regio-, dia-stereo-, and chemoselectivity are the important features of this method. (Diagram presented) (G) Cyclization: Exposure of unsaturated malonates bearing pendant alcohols to Cu(BF 4)2·xH2O10 and Mn(OAc) 3 gives rise to the formation of carbocycles linked to oxygen heterocycles. The use of copper(II) salts bearing poorly coordinating anions has a profound influence on the product distribution. (Diagram presented) (H) Acetal formation: Dimethyl/diethyl acetal formation in high yields from aldehydes and ketones by reaction with trimethyl/triethyl orthoformate at room temperature and in short reaction time has been successfully carried out in the presence of a catalytic amount of Cu(BF4)2·xH 2O which can be recycled. (Diagram presented) (I) 1,3-Dithiolane/dithiane formation: Recently, Cu(BF4) 2·xH2O has emerged as an extremely efficient catalyst for 1,3-dithiolane/ dithiane formation from aromatic, heteroaromatic and aliphatic aldehydes and cyclic saturated ketones under solvent-free conditions at room temperature. (Diagram presented) (J) Carbamate formation: N-tert-Butoxycarbonylation of amines by reaction with di-tert-butyldicarbonate under solvent-free conditions and at room temperature was successfully carried out in the presence of a catalytic amount of Cu(BF4) 2·xH2O in high yield. (Diagram presented) © Georg Thieme Verlag Stuttgart.