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LANTHANOID TRIFLATE-PROMOTED INDIUM- OR ZINC-MEDIATED ALLYLATION OF AMINOALDEHYDE IN AQUEOUS MEDIA: STEREOSELECTIVE ROUTE TO ß-AMINOALCOHOLS

1997; De Gruyter; Volume: 20; Issue: 4 Linguagem: Inglês

10.1515/mgmc.1997.20.4.237

2191-0219

Teck‐Peng Loh, Ruibin Wang, Kee‐Leng Tan, Keng‐Yeow Sim,

Inorganic and Organometallic Chemistry

Lanthanide triflate-promoted indium-or zinc-mediated allylations of αaminoaldehyde in aqueous media have been developed and shown to obtain high level of antidiastereofacial selectivity by the judicious choice of the amino-protecting group, Lewis acid and solvent employed.Lewis acid catalyzed carbon-carbon bond forming reactions are of great interest in organic synthesis because of their unique reactivity and selectivity.Recently, we discovered that lanthanoid triflate increased the reaction rate and diastereofacial selectivity of indium-mediated allylation of a glucose-derived aldehyde and similar coupling allylation reactions of ethyl 4bromocrotonate with carbonyl compounds in aqueous media. 1 We also found that indium trichloride effectively catalyzes Mukaiyama's aldol reaction, Diels-Alder reactions and tin-mediated carbonyl allylations in aqueous media.The respective products were obtained in very good yield and high diastereofacial selectivities. 2 In relation to our continued interest to develop new methodologies in aqueous media, we wish to report herein the lanthanoid triflate-promoted indium-or zinc-mediated allylations of α-aminoaldehyde.This can be achieved with good yields and high levels of anf/-diastereofacial selectivities by the judicious choice of the amino-protecting group, Lewis acid and solvent employed (eq.1).This methodology permits the stereoselective preparation of various chiral ß-amino alcohols which are present in a wide variety of biologically and pharmacologically important compounds. 3 Commercially available and cheap L-leucine was used as the starting material.Benzylation of L-leucine in an aqueous solution of potassium carbonate and sodium hydroxide gave the N,Ndibenzylamino benzyl ester.Reduction with lithium aluminum hydride afforded the corresponding alcohol, followed by a Swern oxidation to give the Ν,Ν-dibenzylaminoaldehyde (1) 4 .