Melvin De Jesús

Highly Enantioselective Borane Reduction of Heteroaryl and Heterocyclic Ketoxime Ethers Catalyzed by Novel Spiroborate Ester Derived from Diphenylvalinol : Application to the Synthesis of Nicotine Analogues

An asymmetric synthesis for the preparation of nonracemic amines bearing heterocyclic and heteroaromatic rings is described. A variety of important enantiopure thionyl and arylalkyl primary amines were afforded by the borane-mediated enantioselective reduction of O-benzyl ketoximes using 10% of catalyst 10 derived from ( S)-diphenylvalinol and ethylene glycol with excellent enantioselectivity, in up to 99% ee. The optimal condition for the first asymmetric reduction of 3- and 4-pyridyl-derived O-benzyl ketoxime ethers was achieved using 30% of catalytic loading in dioxane at 10 degrees C. ( S)- N-ethylnornicotine ( 3) was also successfully synthesized from the TIPS-protected ( S)-2-amino-2-pyridylethanol in 97% ee.

A Practical and Efficient Route for the Highly Enantioselective Synthesis of Mexiletine Analogues and Novel β-Thiophenoxy and Pyridyl Ethers

A practical and efficient procedure for the enantioselective synthesis of mexiletine analogues with use of 10% of spiroborate ester 6 as chirality transfer agent is presented. A variety of mexiletine analogues were prepared in good yield with excellent enantioselectivities (91-97% ee) from readily available starting materials. The developed methodology was also successfully applied for the synthesis of novel beta-amino ethers containing thiophenyl and pyridyl fragments.

Chiral Epoxides via Borane Reduction of 2-Haloketones Catalyzed by Spiroborate Ester: Application to the Synthesis of Optically Pure 1,2-Hydroxy Ethers and 1,2-Azido Alcohols

An enantioselective borane-mediated reduction of a variety of 2-haloketones with 10% spiroaminoborate ester 1 as catalyst is described. By a simple basic workup of 2-halohydrins, optically active epoxides are obtained in high yield and with excellent enantiopurity (up to 99% ee). Ring-opening of oxiranes with phenoxides or sodium azide is investigated under different reaction conditions affording nonracemic 1,2-hydroxy ethers and 1,2-azido alcohols with excellent enantioselectivity (99% ee) and in good to high chemical yield.

Efficient α-alkylation and silylation of aromatic O-tert-butyldimethylsilyl ketoximes

Abstract The α-alkylation and silylation of para substituted acetophenones, 1-and 2-indanone (O-TBS) oximes at various reaction conditions, were studied. Optimum conversions from 82% to 100% were afforded for the alkylation and silylation of these (O-TBS) ketoximes with LDA at −78 °C, using electrophiles, such as, methyl iodide, ethylbromide, benzyl bromide and trimethylchlorosilane.

A General Uncatalyzed Method for the Synthesis of O- Silylated Oximes

Abstract Aldoximes and ketoximes were smoothly and efficiently O-silylated at room temperature with diverse chlorosilanes such as TMSCl, TBSCl, or TIPSCl in dichloromethane or THF, using imidazole as a base to trap the generated hydrochloric acid.