Zinc(II) Perchlorate Hexahydrate Catalyzed Opening of Epoxide Ring by Amines:  Applications to Synthesis of (RS)/(R)-Propranolols and (RS)/(R)/(S)-Naftopidils

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...

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Bibliographic Details
Published in:Journal of organic chemistry 2007-05, Vol.72 (10), p.3713-3722
Main Authors: Shivani, Pujala, Brahmam, Chakraborti, Asit K
Format: Article
Language:English
Subjects:
Amines - chemistry
Catalysis
Catalysts: preparations and properties
Chemistry
Epichlorohydrin - chemistry
Epoxy Compounds - chemistry
Exact sciences and technology
General and physical chemistry
Metals - chemistry
Molecular Structure
Naphthalenes - chemical synthesis
Naphthalenes - chemistry
Noncondensed benzenic compounds
Organic chemistry
Perchlorates - chemistry
Piperazines - chemical synthesis
Piperazines - chemistry
Preparations and properties
Propranolol - chemical synthesis
Propranolol - chemistry
Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
Zinc Compounds - chemistry
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Summary: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.
ISSN:0022-3263
1520-6904
DOI:10.1021/jo062674j