Hydrazone Mannich-type reactions

Hydrazones are much more stable than imines and are often isolated as stable crystals which can be stored at room temperature. A drawback of using hydrazones as electrophiles is fheir low reactivity. Kobayashi et al. have found that ben-zoylhydrazones serve as stable surrogates of unstable imines in Sc(OTf)3-catalyzed Mannich-type reactions (Scheme 10.75) [210]. Benzoylhydrazones derived from aldehydes including functionalized or unstable ones react smoofhly with silyl eno-... 

The Mannich reaction and its variants have been reviewed, mainly focussing on asymmetric catalysis thereof. Catalytic, enantioselective, vinylogous Mannich reactions have also been reviewed, covering both direct and silyl dienolate methods. Another review surveys Mannich-type reactions of nitrones, oximes, and hydrazones. A pyrrolidine-thiourea-tertiary amine catalyses asymmetric Mannich reaction of N-Boc-imines (e.g. Ph-Ch=N-Boc) with ethyl-4-chloro-3-oxobutanoate to give highly functionalized product (16). Addition of triethylamine leads to one-pot intramolecular cyclization to give an 0-ethyl tetronic acid derivative (17). ... 

Imidazoline-anchored phosphine ligand-Zn(II) complexes promote asymmetric Mannich-type reaction of F2C=C(R )OTMS with hydrazones (R CH=NNHCOR ) under mild conditions. ... 

Additions of stabilized carbanions to imines and hydrazones, respectively, have been used to initiate domino 1,2-addition/cyclization reactions. Thus, as described by Benetti and coworkers, 2-subshtuted 3-nitropyrrolidines are accessible via a nitro-Mannich (aza-Henry)/SN-type process [165]. Enders research group established a 1,2-addition/lactamization sequence using their well-known SAMP/ RAMP-hydrazones 2-308 and lithiated o-toluamides 2-307 as substrates to afford the lactams 2-309 in excellent diastereoselectivity (Scheme 2.72) [166]. These compounds can be further transformed into valuable, almost enantiopure, dihydro-2H-isoquinolin-l-ones, as well as dihydro- and tetrahydroisoquinolines. 

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