Organolithium reagent aldimines

The reaction of butyllithium with 1-naphthaldehyde cyclohexylimine in the presence of (/C )-l,2-diphenylethane-1,2-diol dimethyl ether in toluene at —78 °C, followed by treatment with acetate buffer, gave 2-butyl-1,2-dihydronaphthalene-l-carbaldehyde, which was then reduced with sodium borohydride in methanol to afford (1 R,2.S)-2-butyl-1 -hydroxymcthyl-1,2-dihydronaphthalene in 80% overall yield with 91 % ee83. Similarly, the enantioselective conjugate addition of organolithium reagents to several a,/J-unsaturated aldimines took place in the presence of C2-symmetric chiral diethers, such as (/, / )-1,2-butanediol dimethyl ether and (/, / )- ,2-diphenylethane-1,2-diol dimethyl ether. 

The hydroamination of alkynes is an efficient way to obtain aldimines with the advantage of avoiding formation of by-products. As shown in Scheme 8.65, the method has been developed into a multicomponent synthesis of a-branched amines. Aldimines 154 are formed using a titanium derivative as catalyst and reacted in situ with an organolithium reagent [141]. 

The complexes (5,5)-(Phebox)Pt(OTf) and [(5,5)-(Phebox)Pt(H20)](BF4) react with A -phenylbenzaldimine to afford the corresponding chiral aldimine complexes. Addition of organolithium reagents gives, after work-up, the corresponding enantio-merically enriched amines (Sch. 34) [145],... 

Iminium salts bearing a labile trimethylsilyl group can be generated in situ and undergo nucleophilic addition (see Sections 1.12.4.2 and 1.12.7.3). Bis(trimethylsilyl)methoxymethylamine (75), for example, has been used as a formaldehyde equivalent for the preparation of primary amines. Cyclic imines, such as 3,4-dihydroquinolines, react with trimethylsilyl triflate (TMS-OTf) to provide reactive labile iminium salts (55), which condense with picoline anions. The addition of nonstabilized Grignard and organolithium reagents to acyclic aromatic ketimines and aldimines, however, is often not facilitated by the presence of TMS-OTf ... 

Lithium aldimine (131), an acyl anion equivalent derived from an isocyanide and an organolithium reagent, adds to aldehydes giving, after quenching with water, a-amino ketones (134) via the Amadori rearrangement (Scheme 33)." The a-amino ketone (134) results from a double tautomerization of a-hydroxy imine (132), formed initially after quenching with water. Thus, the imine (132) isomerizes to enolamine (133), which in turn tautomerizes to the observed product (134). 

Enolizable A -trimethylsilylaldimines can be generated in situ by the addition of organolithium reagents to bis(trimethylsilyl)formamide. These undergo addition reactions with enolates to form 3-lactams. Phosphonium salts used in catalytic amounts promote the reaction between aryl aldimines and silylketene acetals to form 3-amino esters. Mannich bases with N-2-hydroxyethyl-N-methyl substitution are prepared by the reaction of the iminium salt synthon, 3-methyl-1,3-oxazolidine, with enol silanes in the presence of chloromethylsilanes. ... 

Aliphatic organomagnesium or organolithium reagents add to 1,1,3,3-tetramethylbutyl isocyanide to give the corresponding metallo-aldimine (150), another acyl carbanion equivalent, which reacts with a range of electrophiles in the normal manner. 

Mixed lanthanide-alkali chlorides, LnCl3.2LiCl (Ln = La, Ce, Nd) can be readily prepared as 0.5 mol dm-3 solutions in THF.235 They act as improved promoters of addition of organomagnesium reagents to ketones, and also to aldimines, and in addition have been found to promote organolithium addition. 

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]. 

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