Magnesium aldimines

Isocyanides that do not contain an a hydrogen react with alkyllithium compounds, as well as with Grignard reagents, to give lithium (or magnesium) aldimines. These metalated aldimines are versatile nucleophiles and react with various substrates as follows ... 

Into a 500 ml. three-necked flask, provided with a mechanical stirrer, a gas inlet tube and a reflux condenser, place 57 g. of anhydrous stannous chloride (Section 11,50,11) and 200 ml. of anhydrous ether. Pass in dry hydrogen chloride gas (Section 11,48,1) until the mixture is saturated and separates into two layers the lower viscous layer consists of stannous chloride dissolved in ethereal hydrogen chloride. Set the stirrer in motion and add 19 5 g. of n-amyl cyanide (Sections III,112 and III,113) through the separatory funnel. Separation of the crystalline aldimine hydrochloride commences after a few minutes continue the stirring for 15 minutes. Filter oflF the crystalline solid, suspend it in about 50 ml. of water and heat under reflux until it is completely hydrolysed. Allow to cool and extract with ether dry the ethereal extract with anhydrous magnesium or calcium sulphate and remove the ether slowly (Fig. II, 13, 4, but with the distilling flask replaced by a Claisen flask with fractionating side arm). Finally, distil the residue and collect the n-hexaldehyde at 127-129°. The yield is 19 g. 

Reaction of Various Aldimine and Ketimine Magnesium Bromide Salts with Alkylating Agents in Tetrahydrofuran... 

The physical constants of several other imines prepared by a similar procedure are shown in Table X. The aldimines listed in the Table can be obtained only if certain precautions are strictly observed [4b]. The method of Emerson, Hess, and Uhle [4c] could not be extended satisfactorily and the method described in Preparation 2-2 is a modification of the one described by Chancel [4d] for propylidenepropylamine. The reaction is best carried out by adding the aldehyde to the amine, without a solvent, at 0°C. When the order of addition is reversed, the yields are much lower. Potassium hydroxide is added at the end in order to remove the water formed during the reaction. The use of other drying agents such as potassium carbonate or magnesium sulfate failed to yield aldimines on distillation. The aldimines should always be distilled from fresh potassium hydroxide to yield water-white products. The aldimines are unstable and should be used within a few hours after their distillation otherwise polymeric products are obtained. 

Koga reports that a.P-unsaturated aldimines (89), derived from L-r-leucine r-butyl esters, undergo asymmetric additions with Grignard reagents which is due to formation of a highly ordered magnesium chelate (Scheme 29).75... 

Whiting et al. [20] found the catalytic system for an aza Diels-Alder reaction by the use of a combinatorial approach to catalyst selection. When methyl glyoxylate-derived aldimine 25 was reacted with Danishefsky s diene 24 in the presence of the chiral magnesium catalyst (10 mol %), prepared in-situ from chiral diphenylethylenediamine 23, Mgl2, and 2,6-lutidine, the Diels-Alder product 26 was obtained in 64 % yield with 97 % ee (Sch. 9). 

The reactions of organometallic reagents such as organolithium [696], -zinc [697-700], -magnesium [701], and -aluminum species [702] are facilitated by the presence of TiCU [9] as exemplified in Eq. (308) [703]. Even addition of a titanium compound to aldehydes was promoted in the presence of an extra amount of a titanium salt (Eq. 309) [704,705]. Titanium Lewis acids increase the reactivity of the a-position of a ketone (Eq. 310) [706] and the /3-position of an a,/3-unsaturated carbonyl compound towards nucleophiles (Eq. 311) [608,707-709]. The positive role of TiCU in the photo-hydroxymethylation of ketones and aldimines is ascribed to activation of methanol by the titanium salt (Eq. 312) [710]. 

Some examples of combined syn-anti and diastereofacial selectivity employing /V-n-propyl- and N-isopropyl-aldimines, derived from a-phenylpropionaldehyde, and crotyl-9-BBN, -magnesium and -zirconium reagents have been reported by Yamamoto et al. Cram selectivity, which is observed in the analogous reactions of these chiral imines with allyl organometallics (see Section 4.3.2.1.2i), is preserved as ratios of Cram anti-Cram products are consistently about 8 1. Anti selectivity is also observed but the ratios do not exceed 7 3. The weak anti selectivity parallels that observed in reactions of crotyl-9-BBN with branched a-alkylaldimines. Since syn-anti selectivity is influenced more by the a-substituent than by the A-substituent of the aldimine, more synthetically useful levels of combined syn-anti and diastereofacial selectivity might be expected in other series of a-substituted aldimines. 

Magnesium iodide. 20, 232 Pyrrolidines. Pyrrolidine -caction with aldimines, are caia 4rc similarly obtained. 

A highly q -selective and enantioselective direct Mannich-type reaction of aldimines 32 and trichloromethyl ketones 33 was developed by Shibasaki using a chiral Pybox (31)-lanthanum(m) lithium(i) heterobimetallic catalyst (Scheme 2.23). The 2-thiophenesulfonyl moiety of 32 can be readily removed by using magnesium metal. Moreover, a trichloromethyl ketone moiety can be transformed to ester, dithiane, and syn- and anti-trichloromethyl carbinols in high yields. 

Aldimines (R -CH=N-R ) have been phosphinated with diphenylphosphine oxide to give a-amino phosphine oxides (42) in up to 99% ee, using a chiral magnesium phosphate catalyst. ... 

Fig. 22 Magnesium complex bearing an anilide-aldimine ligand, NNN and coworkers [82]...

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