Mannich-Type Reactions Using Hydrazones

The /5-N -benzoylhydrazino esters were readily converted into a variety of N-con-taining compounds. Reductive cleavage of the nitrogen-nitrogen bond of the hydra-zino compounds was successfully conducted by use of Raney Ni under a H2 atmosphere [14] to afford the /8-amino esters. Cyclization of y8-Al -benzoylhydrazino esters was conducted under basic conditions /i-lactams were obtained by treatment with n-BuLi at -78 °C, whereas pyrazolones were produced in the presence of NaOMe in MeOH at room temperature or under reflux (Sch. 4). 

It was also found that in the presence of a catalytic amount of Sc(OTf)3 benzoylhydrazones reacted with tetraallyltin to afford the corresponding homoallylic hydrazines these were readily converted to homoallylic amines. Three-component reactions of aldehydes, benzoylhydrazine, and tetraallyltin also proceeded smoothly in the presence of a catalytic amount of Sc(OTf)3 [15]. 

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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-... 

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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