Imines from

Tetracyelie derivatives 215 formed exclusively from imines 213 on the action of TMSOTf, whereas in the presence of TiCl4 both l//-pyrido[l,2-c]quinazolin-6-ones 214, as a >9 1 mixture of a//3 ehloro epimers, and tetraeyelie derivatives 215 were obtained. Imine 213 (R = H) gave a 3 1... 

Of course, the key limitation of the ylide-mediated methods discussed so far is the use of stoichiometric amounts of the chiral reagent. Building on their success with catalytic asymmetric ylide-mediated epoxidation (see Section 1.2.1.2), Aggarwal and co-workers have reported an aza version that provides a highly efficient catalytic asymmetric synthesis of trans-aziridines from imines and diazo compounds or the corresponding tosylhydrazone salts (Scheme 1.43) [68-70]. 

Volume E21 D.1.3.5.1. Addition of Azaenolates from Imines or Nitrogen Heterocycles... 

In general, metalated 2-azaallyl anions derived from imines of a-amino esters serve both as Michael donors and as 1,3-dipolar reagents the course of the reaction, as well as the stereochemical outcome depends upon the base and the reaction conditions82,83. 

Dipolar [3 + 2] cycloadditions are one of the most important reactions for the formation of five-membered rings [68]. The 1,3-dipolar cycloaddition reaction is frequently utihzed to obtain highly substituted pyrroHdines starting from imines and alkenes. Imines 98, obtained from a-amino esters and nitroalkenes 99, are mixed together in an open vessel microwave reactor to undergo 1,3-dipolar cycloaddition to produce highly substituted nitroprolines esters 101 (Scheme 35) [69]. Imines derived from a-aminoesters are thermally isomerized by microwave irradiation to azomethine yhdes 100,... 

The addition of Grignard reagents to aldehydes, ketones, and esters is the basis for the synthesis of a wide variety of alcohols, and several examples are given in Scheme 7.3. Primary alcohols can be made from formaldehyde (Entry 1) or, with addition of two carbons, from ethylene oxide (Entry 2). Secondary alcohols are obtained from aldehydes (Entries 3 to 6) or formate esters (Entry 7). Tertiary alcohols can be made from esters (Entries 8 and 9) or ketones (Entry 10). Lactones give diols (Entry 11). Aldehydes can be prepared from trialkyl orthoformate esters (Entries 12 and 13). Ketones can be made from nitriles (Entries 14 and 15), pyridine-2-thiol esters (Entry 16), N-methoxy-A-methyl carboxamides (Entries 17 and 18), or anhydrides (Entry 19). Carboxylic acids are available by reaction with C02 (Entries 20 to 22). Amines can be prepared from imines (Entry 23). Two-step procedures that involve formation and dehydration of alcohols provide routes to certain alkenes (Entries 24 and 25). 

This system also worked well in ionic liquids.518 Li etal. found silver-phosphine complexes to promote aldehyde-alkyne coupling in water. When triphenylphosphinesilver chloride was used as a catalyst in water, the only detected product was the aldehyde addition product instead of the adduct derived from imine (Scheme 111).519... 

Chiral a-amino acids from imines derived from (S)-menthone... 

Five configurationally known oxaziridines derived from imines of PEA display nonequivalence behavior that is in general accord with this model, though occasional unpredictable deviations attributed to internal magnetic anisotropic effects were noted (41). 

Fig. 4.9. Formation and transformations of azomethine ylides from imines and electrophilic carbene complexes.

This procedure is an adaptation of that described by Emmons for the preparation of oxaziranes from imines using peracetic acid. Other procedures which may be more useful for oxazirane preparation in specific instances are the oxidation of imines with iw-chloroperbenzoic acid and the reaction of aldehydes or ketones with hydroxylamine 0-sulfonic acid in alkaline solution. 2-<-Butyl-3-phenyloxazirane has also been prepared by photolysis of a-phenyl-N-f-butylnitrone (a general reaction of considerable theoretical interest since it represents direct conversion of electromagnetic energy to chemical energy) and in low yields by ozonoly-sis of N-f-butylbenzaldimine. ... 

Figure 2.5 K. values for amplified compounds from imine DCLs.

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