Additive Effects on Asymmetric Catalysis

Abstract

This review highlights a number of additives that can be used to make asymmetric reactions perfect. Without changing other reaction conditions, simply adding additives can lead to improved asymmetric catalysis, such as reduced reaction time, improved yield, or/and increased selectivity.

Naked d-orbital in a centrochiral Ni(II) complex as a catalyst for asymmetric [3+2] cycloaddition

“…Intriguingly, the diamine 4e has been overlooked as a chiral ligand for over a decade despite its potential utility and simplicity42. We finally found that diisopropylamine ( i Pr 2 NH: 10 mol%) can further improve not only the reactivity, but also the enantioselectivity43, affording (1 R ,2 R ,10b S )- 3aa in 71% yield, >50/1 d.r. and 91% e.e., with 5 mol% of Ni(OAc) 2 ·4H 2 O–( R,R )- 4e (Table 1, entry 14).…”

Enantioselective synthesis of seven-membered carbo- and heterocyles by organocatalyzed intramolecular Michael addition

“…The variation of stereoselection with the nature of the counterion, which is dependent on the acid used as co-catalyst is a very well known act in organocatalytic transformations. 21 The acid additive accelerates the formation of iminium ion, and in the present case the drop in the enantioselection could be attributed to the extension in which the uncatalyzed background cyclization occurs.…”

Catalytic asymmetric synthesis of CF3-substituted tertiary propargylic alcohols via direct aldol reaction of α-N3amide

“…Further investigation of various additives 40 showed the beneficial effect of MS13X on the reactivity and selectivities (entries 9–13). As other additives such as MS3A and 4A afforded lower yields, MS13X is less likely to serve as a simple desiccant in this case ( vide infra ).…”