Lithium phosphonate umpolung catalysts: Do fluoro substituents increase the catalytic activity?

• Anca Gliga,
• Bernd Goldfuss and
• Jörg M. Neudörfl

Beilstein J. Org. Chem. 2011, 7, 1189–1197, doi:10.3762/bjoc.7.138

• decreased catalytic activity for the fluorinated precatalysts compared to the nonfluorinated systems is observed. Furthermore, the ring size of six, seven and nine membered ring catalysts appears not to be crucial for their catalytic activity. Keywords: benzoin coupling; catalytic activity; fluoro effects

• comparable activities for lithium phosphonate and cyanide [19][20]. Recently, we introduced fenchol based phosphonates as precatalysts, which are similarly accessible as fencholate metal catalysts [21][22][23][24][25], in the benzoin coupling (Scheme 2) [26]. A strong increase of the catalytic activity was

• comparison of fluorinated and nonfluorinated TADDOL phosphonates (which were used by Johnson's group) as precatalysts in benzoin coupling does not show any difference in reactivity (Scheme 2). In contrast the enantioselectivity is clearly higher with the fluorinated TADDOL precatalyst (Scheme 2). Here, we