18366-43-3Relevant articles and documents
Zinc(II) perchlorate hexahydrate catalyzed opening of epoxide ring by amines: Applications to synthesis of (RS)/(R)-propranolols and (RS)/(R)/(S)-naftopidils
Shivani,Pujala, Brahmam,Chakraborti, Asit K.
, p. 3713 - 3722 (2007)
(Figure Presented) Commercially available zinc(II) Perchlorate hexahydrate [Zn(ClO4)2·6H2O] was found to be a new and highly efficient catalyst for opening of epoxide rings by amines affording 2-amino alcohols in high yields under solvent-free conditions and with excellent chemo-, regio-, and stereoselectivities. For unsymmetrical epoxides, the regioselectivity was influenced by the electronic and steric factors associated with the epoxides and the amines. A complementarity in the regioselectivity was observed during the reaction of styrene oxide with aromatic and aliphatic amines: aromatic amines provided amino alcohols from nucleophilic attack at the benzylic carbon as major products whereas aliphatic amines resulted in formation of the amino alcohols through reaction at the terminal carbon atom of the epoxide ring as the major/sole products. Reaction of aniline with various glycidic ethers gave the amino alcohols by regioselective nucleophilic attack at the terminal carbon atom of the epoxide ring as the only/major product. Zinc(II) Perchlorate hexahydrate was found to be the best catalyst compared to other metal Perchlorates. The counteranion modulated the catalytic property of the various Zn(II) compounds that followed the order Zn(ClO4) 2·6H2O Zn(BF4)2 ～ Zn(OTf)2 ZnI2 > ZnBr2 > ZnCl2 > Zn(OAc)2 > Zn(CO3)2 in parallelism with the acidic strength of the corresponding protic acids (except for TfOH). The applicability of the methodology was demonstrated by the synthesis of cardiovascular drugs propranolol and naftopidil as racemates and optically active enantiomers.
A cobalt catalyzed protocol for the synthesis of substituted β-phenyl isoserine derivatives
Bhatia, Beena,Jain, Swati,De, Asit,Bagchi, Ipsita,Iqbal, Javed
, p. 7311 - 7314 (1996)
A versatile cobalt catalyzed protocol for the epoxidation of α,β unsaturated esters or amides followed by its cleavage with aniline and its derivatives to afford substituted β-phenyl isoserine derivative has been developed.
Zinc tetrafluoroborate hydrate as a mild catalyst for epoxide ring opening with amines: Scope and limitations of metal tetrafluoroborates and applications in the synthesis of antihypertensive drugs (RS)/(R)/(S)-metoprolols
Pujala, Brahmam,Rana, Shivani,Chakraborti, Asit K.
experimental part, p. 8768 - 8780 (2011/12/04)
The scope and limitations of metal tetrafluoroborates have been studied for epoxide ring-opening reaction with amines, and Zn(BF4) 2?xH2O has been found to be a mild and efficient catalyst affording high yields under solvent-free conditions at rt with excellent chemo-, regio-, and stereoselectivities. The catalytic efficiency followed the order Zn(BF4)2?xH2O ? Cu(BF4)2?xH2O > Co(BF4) 2?6H2O ? Fe(BF4)2? 6H2O > LiBF4 for reactions with cyclohexene oxide and Zn(BF4)2?xH2O ? Co(BF4) 2?6H2O ? Fe(BF4)2? 6H2O > Cu(BF4)2?xH2O for stilbene oxide, but AgBF4 was ineffective. For reaction of styrene oxide with aniline, the metal tetrafluoroborates exhibited comparable regioselectivity (1:99-7:93) with preferential reaction at the benzylic carbon of the epoxide ring. A reversal of regioselectivity (91:1-69:31) in favor of the reaction at the terminal carbon of the epoxide ring was observed for reaction with morpholine. The regioselectivity was dependent on the electronic and steric factors of the epoxide and the pKa of the amine and independent of amine nucleophilicity. The role of the metal tetrafluoroborates is envisaged as "electrophile nucleophile dual activation" through cooperativity of coordination, charge-charge interaction, and hydrogen-bond formation that rationalizes the catalytic efficiency, substrate reactivity, and regioselectivity. The methodology was used for synthesis of cardiovascular drug metoprolol as racemic and enriched enantiomeric forms.
