Imines Lewis acid mediated

The diastereofacial selective imine-ene reactions with a-imino esters prepared from (—)-8-phenylmenthyl glyoxylate have provided an efficient entry to the asymmetric synthesis of a-amino acids, and a Lewis acid-mediated intramolecular imine-ene reaction has been used for the key spirocyclization step in a recent synthesis of (—)-perhydrohistrionicotoxin. Asymmetric azo-ene reactions have been effected using the chiral azo-enophile, di-(—)-(lR,2S)-2-phenyl-l-cyclohexyldiazenedicarboxylate. ... 

The development of new methods for the synthesis of homoallylic amine derivatives is an important area of synthetic efforts. Homoallylic amines are extremely important compounds as biologically active molecules [1], The Lewis acid-mediated reactions of imines with allyl silanes are among the most efficient for... 

One approach to tetrahydropyridinones is the Lewis acid mediated hetero-Diels-Alder reaction of electron-rich dienes with polystyrene-bound imines (Entries 3 and 4, Table 15.23). The Ugi reaction of 5-oxo carboxylic acids and primary amines with support-bound isonitriles has been used to prepare piperidinones on insoluble supports (Entry 5, Table 15.23). Entry 6 in Table 15.23 is an example of the preparation of a 4-piperidinone by amine-induced 3-elimination of a resin-bound sulfinate followed by Michael addition of the amine to the newly generated divinyl ketone. The intramolecular Pauson-Khand reaction of propargyl(3-butenyl)amines, which yields cyclopenta[c]pyridin-6-ones, is depicted in Table 12.4. 

Table 4 Ratio of Diastereoisomers in the Lewis Acid Mediated Reactions of Silyl Ketene Acetals with Imines...

Cook and Stille investigated the aza-Cope rearrangement of the V-allyl enamine (355). The Lewis acid-mediated rearrangement of (355) resulted in the formation of the corresponding imine, which... 

Oxidation of Imines. The oxidative rearrangement of A -aryl-aldimines leads to amides upon treatment with m-CPBA and BF3 OEt2 (eq 51). The reaction presumably proceeds via the Lewis acid mediated peracid imine adduct which then loses m-chlorobenzoic acid. 

A Lewis acid mediated reaction of acyclic vinyl allenes and imines to produce tetrahydropyridines was developed by Palenzuela and coworkers in 2012 [9]. The cycloadducts can be transformed into polysub-stituted pyridines, including bipyridines, by catalytic transfer... 

This book chapter is limited to Lewis acid-mediated reactions, and does not discuss the important field of Lewis base-mediated allylations, nor does it describe the reactions of allylsilanes with other electrophiles such as epoxides, imines, and allyl-X (X = -Cl, -OR, -OAc). The SaJcurai reaction has been covered under different forms in reviews focusing on The Stereochemistry of the Sakurai reaction , Intramolecular Addition Reactions of Allylic and Propargylic Silanes ," Selective Reactions Using Allylic Metals , Catalytic Enantioselective Addition of Allylic Organometallic Reagents to Aldehydes and Ketones , and Modem Carbonyl Chemistry . ... 

Two papers have appeared on carbohydrate approaches to polyhydroxylated quinolizidines. The key step in the synthesis of 165 was a diastereoselective Lewis acid-mediated addition to imine 164 derived from D-arabinose (Scheme 34). ... 

Probably the most widely applicable asymmetric imine aziridination reaction reported to date is that of Wulff et al. These workers approached the reaction from a different perspective, utilizing the so-called vaulted , axially chiral boron Lewis acids VANOL and VAPOL [35] to mediate reactions between ethyl diazoacetate and N-benzhydrylimines (Scheme 4.29) [36]. The reactions proceed with impressive enantiocontrol, but there is a requirement that the benzhydryl substituent be present since this group is not an aziridine activator there is, therefore, a need for deprotection and attachment of a suitable activating group. Nonetheless, this method is a powerful one, with great potential for synthesis, as shown by the rapid synthesis of chloroamphenicol by the methodology [37]. 

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