Lithium trialkylzincates

The addition of alkyllithium, lithium dialkylcuprates and lithium trialkylzincates to either ( )-(2-nitroethenyl)benzene or E)- -nitropropene in the presence of the nonracemic chiral solvent, ( + )-(S,S)-2,3-dimethoxy-Af,AhA, iV -tetramethyl-l,4-butanediamine, gave adducts in low enantiomeric excess (15-28%) as determined by HNMR35. 

SCHEME 31. Preparation and uses of allenic zinc reagents using lithium trialkylzincates... 

Lithium butyldimethylzincate, 221 Lithium sec-butyldimethylzincate, 221 Lithium-Ethylamine, 158 Lithium o-lithiophenoxide, 166 Lithium methoxyacetylide, 166 Lithium phenylacetylide, 244 Lithium trialkylzincates, 221 Lithium trimethylsilylacetylide, 206 Lithium trimethyl(tributylstannyl)-aluminate, 320... 

Zincate carbenoids. Reaction of lithium trialkylzincates with a 1,1-dibro-moalkane results in a double insertion into the C-Br bonds to provide a secondary zincate carbenoid.2 These products undergo Pd-catalyzed coupling with acid chlorides or vinyl bromides. 

Lithium trialkylzincates (8, 515-516).4 1,1-Dibromoalkenes react with LiR3Zn by a Br/Zn exchange at - 85° to form a 1-bromoalkenylzincate (a), which undergoes. in intramolecular alkylation in the presence of acetic acid at 0°. The alkylation involves at least partial inversion at the carbenoid carbon. 

Method To a solution of lithium trialkylzinc (1.0 mmol) in THF (3.5 mL) was added 1,1-dibromocy-clopropane (0.8 mmol) at 0°C under N2, and the resulting mixture was stirred for 0.5 h at 0°C. The mixture was then hydrolyzed with dil HCl, extracted with Et20, dried, and the product isolated by flash chromatography. 

Method C. To a solution of 1,1-dibromocyclopropane (0.8 mmol) in THF (3.5 mL) was slowly added a hexane solution of BuLi (l.Ommol) at — 85 C under Nj. To this solution was added at — 85 C, hexa-chloroethane or l,l,2-trichloro-l,2,2-trifluoroethane (Freon-113) and the mixture was stirred at — 85°C for 0.5 h. To this was added a THF (3.5 mL) solution of lithium trialkylzinc (1.3 mmol) and the mixture was warmed from — 85 C to rt during a period of 3 h and stirred for a further 0.5 h at the same temperature. The mixture was then hydrolyzed with dil HCl, extracted with EtjO, dried, and the product isolated by flash chromatography. 

The lithium trialkylzinc reagents LiZnR3 prepared from RLi and zinc(ll) chloride effect the conjugate addition of an alkyl group (R) to a/8-unsaturated ketones. The acid-catalysed addition of some secondary amines to monoactivated cyclopropyl ketones has been examined. ... 

Immobilized zincates such as 177 can be prepared by treating serine-bound 4-iodobenzoate with t-BujZnLi at 0°C. They react readily with aldehydes. Transme-tallation with lithium (2-thienyl)cyanocuprate provides the copper species 178 that undergoes 1,4-additions. Lithium trialkylzincates can be used for the preparation of benzylic zinc reagents using a very elegant approach of Harada. Thus, the treat-... 

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