Palladacyclic Imidazoline鈥揘aphthalene Complexes: Synthesis and Catalytic Performance in Pd(II)-Catalyzed Enantioselective Reactions of Allylic Trichloroacetimidates
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- 作者：Jeffrey S. Cannon ; James H. Frederich ; Larry E. Overman
- 刊名：The Journal of Organic Chemistry
- 出版年：2012
- 出版时间：February 17, 2012
- 年：2012
- 卷：77
- 期：4
- 页码：1939-1951
- 全文大小：563K
- 年卷期：v.77,no.4(February 17, 2012)
- ISSN：1520-6904
文摘
A new family of air- and moisture-stable enantiopure C,N-palladacycles (PIN-acac complexes) were prepared in good overall yield in three steps from 2-iodo-1-naphthoic acid and enantiopure 尾-amino alcohols. Three of these PIN complexes were characterized by single-crystal X-ray analysis. As anticipated, the naphthalene and imidazoline rings of PIN-acac complexes 18a and 18b were canted significantly from planarity and projected the imidazoline substituents R1 and R2 on opposite faces of the palladium square plane. Fifteen PIN complexes were evaluated as catalysts for the rearrangement of prochiral (E)-allylic trichloroacetimidate 19 (eq 2) and the SN2鈥?allylic substitution of acetic acid with prochiral (Z)-allylic trichloroacetimidate 23. Although these complexes were kinetically poor catalysts for the Overman rearrangement, they were good catalysts for the allylic substitution reaction, providing branched allylic esters in high yield. However, enantioselectivities were low to moderate and significantly less than that realized with palladacyclic complexes of the COP family. Computational studies support an anti-acetoxypalladation/syn-deoxypalladation mechanism analogous to that observed with COP catalysts. The computational study further suggests that optimizing steric influence in the vicinity of the carbon ligand of a chiral C,N-palladacycle, rather than near the nitrogen heterocycle, is the direction to pursue in future development of improved enantioselective catalysts of this motif.