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

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]

References

• 1 Lin G.-q. Hong R. J. Org. Chem.  2001,  66:  2877 
• 2 Trost BM. Pinkerton AB. J. Org. Chem.  2001,  66:  7714 
• 3a Aoyagi S. Wang T.-C. Kibayashi C. J. Am. Chem. Soc.  1993,  115:  11393 
• 3b Halterman RL. Zhu C. Tetrahedron Lett.  1999,  40:  7445 
• 4 Dhawan D. Grover SK. Synth. Commun.  1992,  22:  2405 
• 5 Jefford CW. Jaggi D. Bernardinelli G. Boukouvalas J. Tetrahedron Lett.  1987,  28:  4041 
• 6 Khurana JM. Kukreja G. Synth. Commun.  2002,  32:  1265 
• 7 Rowley M. Tsukamoto M. J. Am. Chem. Soc.  1989,  111:  2735 
• 8 Yakabe S. Hirano M. Morimoto T. Tetrahedron Lett.  2000,  41:  6795 
• 9 Tabaei S.-MH. Pittman CU. Mead KT. J. Org. Chem.  1992,  57:  6669 
• 10a Kyler KS. Watt DS. J. Am. Chem Soc.  1983,  105:  619 
• 10b Kyler KS. Bashir-Hashemi A. Watt DS. J. Org. Chem.  1984,  49:  1084 
• 11 Mukaiyama T. Soga T. Takenoshita H. Chem. Lett.  1989,  997 
• 12 Zim D. Monteiro AL. Tetrahedron Lett.  2002,  43:  4009 
• 13 Lu J. Bai Y. Synthesis  2002,  466 
• 14 Tufariello JJ. Meckler H. Pushpananda K. Senaratne A. Tetrahedron  1985,  41:  3447 
• 15 Terao J. Watanabe H. Ikumi A. Kuniyasu H. Kambe N. J. Am. Chem. Soc.  2002,  124:  4222 
• 16a Chen C. Synlett  2000,  10:  1490 
• 16b Kotora M. Matsumura H. Takahashi T. Chem. Lett.  2000,  3:  236 
• 17 Kiyoi T. Seko N. Yoshino K. Itot Y. J. Org. Chem.  1993,  58:  5118 
• 18 Wu H. Chen R. Zhang Y. Synth. Commun.  2002,  32:  189