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7.6.9.6 Method 6: Addition to Imines

DOI: 10.1055/sos-SD-007-00524

Yanagisawa, A.Science of Synthesis, (20047563.

The reaction of organometallics with imines is a favorable method of preparing secondary amines, and allylic Grignard reagents are among those utilized for this purpose. Among Grignard reagents, allylic magnesium halides have been most frequently applied in the addition to imines because the resulting homoallylic amines can be further transformed into various biologically important molecules such as β-lactams.[‌43‌,‌47‌,‌53‌] Treatment of chiral N-benzylidene-4-toluenesulfinamide 37 with allylmagnesium bromide provides the optically active homoallylic amine derivative 38 as a single diastereomer, and this has been efficiently converted into the chiral β-amino acid 39 in a four-step sequence (Scheme 11).[‌54‌] Camphor-derived chiral sulfinimines also show high stereoselectivity in their reaction with allyl Grignard reagents.[‌55‌] Allylic magnesium halides also react with iminium salts and various N-heterosubstituted imines such as oximes, sulfenimines, and N-(trimethylsilyl)imines.[‌53‌] The reaction of γ-substituted allylic metal reagents with imines produces an α-adduct (linear type of product) and/or a γ-adduct (branched type of product). In general, γ-substituted allylic magnesium reagents tend to preferentially give the γ-adduct, although the syn/anti selectivities obtained in the γ-allylation are not practically useful.[‌53‌]

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