Hydrazone zincated

Organomagnesium compounds react with imines, prepared from 3-methoxy-2-naphth-aldehydes by a 1.4-addition mechanism. This reaction can be performed with high diastere-oselectivity. The method was applied for the synthesis of optically pure S-tetralones . Vinyhnagnesium bromide reacts as an acceptor with a ketone dimethyl hydrazone zincate 207, yielding a 1,1-bimetallic species, which can be reacted sequentially with two different electrophiles (equations 131 and 132) . The reaction proceeds via a metalla-aza-Claisen rearrangement, where the dimethylhydrazone anion behaves as an aza-allylic system . 

In another one-pot process, Nakamura has developed a novel synthesis of pyrroles through the [3+2] coupling of a ketone hydrazone 5 and a vinyistannane <99OL1505>. In this procedure, zincated hydrazone 6 is converted to the gem-Zn/Sn dimetallic intermediate 7 which upon exposure to oxygen directly affords the l-(dimethylamino)pyrroles 8. 

H. 1,1-Dimetal Species from Zincated Hydrazone and Alkenylmetal. 675... 

Nakamura and coworkers showed that the addition reaction of zincated hydrazone to vinylmagnesium halide as electrophile gives the s/r1-geminated organodimetal reagent (Scheme 37). The reaction pathway can be considered as a metalla-aza-Claisen-type... 

As shown in equation 53, when the zincated hydrazone, prepared from hydrazone by treatment with 2 equivalents of f-butyllithium and zinc(II) bromide, is treated with alkenylborane, the a-borylorganozinc is obtained with high diastereoselectivity. This pseudo-gem-dimetal species reacts with allyl halide stereospecifically. Through the transformation, three stereogenic centers are constructed diastereoselectively77. 

Nakamura E, Kubota K, Sakata G, Addition of zincated hydrazone to vinyl grignard reagent, Ketone synthesis by one-pot assembly of four components, J. Am. Chem. Soc., 119 5457-5458, 1997. 

Vinylmagnesium bromide reacts as a Michael acceptor with a zincated hydrazone, yielding a 1,1-bimetallic species, which in some cases can be sequentially trapped with two different electrophiles.246 2463 The reaction proceeds via metalla-aza-Claisen rearrangement. The dimethyl hydrazone anion behaves as an azaallylic system (Scheme 81).247 Vinylphosphonium salts add Grignard reagents, forming alkylphosphonium ylides. These ylides... 

A stereoselective synthesis of substituted pyrrolidines has been achieved by a sequential domino Michael addition and intramolecular carbozincation. The intermediate zinc-copper reagent obtained after cyclization can be trapped with an electrophile such as allyl bromide (Scheme 18).180 Addition of zincated hydrazones 52 on alkenyl boronates, followed by a trapping with an electrophile, provides adduct of type 53 with good yield and high diastereoselectivity (Scheme 19).181 By this addition/trapping sequence, several contiguous stereogenic centers are created in one step. 

Nakamura et al. reported that zincated hydrazones react with vinyl Grignard reagent to afford gem-dimetal compounds. These were treated with benzaldehyde to give alkenyl hydrazones (Scheme 5.22) [29]. 

Similarly, zincated hydrazone derivatives of type 56 undergo an intermolecular carbozincation of strained cyclopropene rings such as 57 leading to the adduct 58 with 92% yield [63]. This type of addition can be extended to ethylene ]63c]. It proceeds with an excellent stereoselectivity allowing the enantioselective synthesis of a-substituted ketones. Allylic zinc species also add to cyclopropenone acetals... 

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