Stereoselective Allylation Reactions of Imines and Related Compounds

Abstract

The stereoselective allylation of imines and related compounds is one of the most effective methods for the introduction of an amino group into carbon skeletons. Moreover, by extending the process to other C=N functionalities such as oximes, hydrazones, nitrones and iminium ions, a variety of nitrogen-containing functional groups can be prepared with the concomitant introduction of the allyl moiety. In several instances it is possible to achieve a complete stereocontrol by using different organometallic reagents. In other cases, either the protective group tuning or the reaction time is crucial for the stereoselectivity of the reaction. This review covers the evolution of stereoselective allylation of imines and related compounds, including oximes, hydrazones, nitrones and iminium ions, from the use of allylic organometallic reagents over chiral substrates up to the recent development of enantioselective methods.

Synthesis of Homoallylamines Enabled by Cobalt or Palladium Catalyzed Allylic Substitution of Azaarylmethylamines

“…Traditional methods to access homoallylamines mainly focus on Lewis acid mediated addition of allyl organometallic reagents to independently prepared imines (Scheme a); however, this method requires prefunctionalized nucleophiles such as allylmagnesiums, , allylsilanes, allylgermanes or allylstannanes, etc . As a valuable alternative, the transition-metal-catalyzed allylic substitution reaction has emerged as a powerful method to construct C–C bonds since Tsuji’s and Trost’s seminal work. , And the transition-metal-catalyzed (Pd, Cu, Rh, Ir, Zn, In, and Yb) formal allylations of imines have been extensively developed via an umpolung strategy (Scheme b).…”

Sequential Nucleophilic Addition/Intramolecular Cycloaddition to Chiral Nonracemic Cyclic Nitrones: A Highly Stereoselective Approach to Polyhydroxynortropane Alkaloids

“…In order to access heavily hydroxylated nortropanes, we selected nitrone 1 (Scheme ), readily prepared from d -arabinose in four steps, for this study. The planned strategy involves allylation of nitrone 1 followed by oxidation and further intramolecular 1,3-dipolar cycloaddition of the resulting alkenyl nitrone. , …”

Homoallyllic Nitrone Isomerization: Convenient Enantioselective Synthesis of Homoallylic Nitrones and Homoallylic Hydroxylamines

“…Homoallylic amines are versatile synthons in synthetic chemistry since the allyl group can be readily converted into a wide variety of synthetically useful compounds . Among the many methods available, enantioselective allylation of imines is one of the most straightforward and efficient methods to obtain homoallylic amines. , However, enantioselective imine allylation has its drawbacks as the allylation of enolizable imines can be complicated with side reactions (Figure ). , Furthermore, the allylations were mostly γ-regioselective, affording branched homoallylic amines. As far as we know, there has been no report on α-regioselective imine allylation with good enantioselectivity.…”

“…We have also demonstrated the versatility of the homoallylic nitrone 3a (Scheme ). It can be readily converted into linear homoallylic amine 6 , which is widely used in synthesis . More importantly, 3a can be readily converted into homoallylic hydroxylamine 5 , a valuable synthon which can easily be transformed into a diverse array of nitrones for various 1,3 dipolar reactions …”