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Synlett 2003(2): 0279-0280
DOI: 10.1055/s-2003-36809
SPOTLIGHT
© Georg Thieme Verlag Stuttgart · New York

NiCl2 and NiCl2 = 6H2O: A very Useful Mild Lewis Acid in Organic Synthesis

Philippe Labrie*
Department of Chemistry, Universitè Laval, Quebec G1K 7P4, Canada
e-Mail: plabrie16@hotmail.com;

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Publication History

Publication Date:
22 January 2003 (online)

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Biographical Sketches

P. Labrie was born in 1977, received his BSc degree in Chemistry (2000) from Laval University, Québec, Canada. Currently he is doing a PhD under the tutelage of Dr. René C.-Gaudreault, Laval University, Québec, Canada and Dr. Suman Rakhit, MCR Research Inc, Toronto, Ontario, Canada. His present research interest is the development of anticancer agents and inhibitors of P-glycoprotein. He is also investigating the application of Michael-type addition of arylboronic acids to enones derived from carbohydrates.

Introduction

Lewis acids are very useful reagents in organic synthesis. The classical Lewis acids currently used include BF3 ·ΟEt2, ZnCl2, SnCl2, TiCl4 and many others. Nickel chloride can be also added to this list. NiCl2 is a mild Lewis acid that promotes a wide variety of organic transformations in aqueous medium or organic solvent and may be used either catalytically or stoichiometrically. NiCl2 was also used in a key step in the synthesis of bi­benzopyran-4-ol, [1] tetrahydrodicranenone B [2] and Allo­pumiliotoxins. [3] NiCl2 is a selective reductive agent when used with hydrides such as LiAlH4 and NaBH4. In fact, the mixture of NiCl2 and NaBH4 is used to prepare nickel boride, [4] a reducing agent for many functional groups: azide, [5] nitrile, [6] NO bond, [7] alkene [8] and haloalkane. [9] NiCl2 was used in the regioselective rearrangement of dienols, [10] ring-opening of epoxide, [11] nickel(II)/chromium(II) chlor­ide-mediated addition to aldehydes or ketones, [2] [3] Suzuki cross-coupling, [12] Biginelli reaction, [13] reductive Heck-like reactions, [14] nickel-catalyzed cross-coupling reaction of Grignard reagents [15] and homo-coupling reactions. [16]

Abstract

(A) Suzuki cross-coupling with ArBr and ArI can be carried out with PhB(OH)2 in good yields using NiCl2 ·6H2O as a catalyst precursor. [12]

(B) NiCl2-(1,3-butadiene) catalyzes the cross-coupling reaction of alkyl chlorides, bromides, and tosylates with Grignard reagents under mild conditions. [15]

(C) A general and convenient preparation of unsymmetrical N,N′-carbodiimides was achieved by the nickel(II)-catalyzed reaction of isocyanides with primary amines using molecular oxygen as an oxidant. [17]

(D) Aryl halides are readily homocoupled using a catalytic amount of NiCl2/CrCl2 and bipyridyl-type ligand 1 in the presence of manganese at room temperature in good yield. [16a]

(E) Azides are efficiently reduced to the corresponding amines with Sm/NiCl2 ·6H2O in excellent yields under mild conditions. [18]

(F) Nitriles are rapidly reduce to primary amines with nickel boride at room temperature. [6]

(F) A Biginelli reaction was efficiently used for the synthesis of 3,4-dihydropyrimidinones from aldehydes, β-keto esters and urea in ethanol, using NiCl2 ·6H2O. [13]

(G) An intramolecular Nozaki-Kishi cyclization was efficiently employed in the cyclization of Z-vinyl bromides to the corresponding cyclopentenols in good yields. [2]

(H) In the presence of moist alumina, aliphatic and aromatic alkenes were hydrogenated quantitatively to alkanes under mild conditions with NaBH4/NiCl2. [8]

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