TMEDA complexes Grignard reagents

Whereas THF and DME were suitable solvents, Lewis basic additives such as HMPA, DMSO or TMEDA hampered the reaction.82 These results point towards an intramolecular assistance of the zinc coordinated by the nitrogen atom. A related effect was evidenced in the additions of Grignard reagents to allylic alcohols83-87. Two mechanisms were proposed for the allylzincation of homoallylic amines involving formation of a complex with the... 

Feringa reports that alkyl heterozincates (131), made from zinc chloride-TMEDA complex, potassium f-butoxide and alkyl Grignard reagents in ether (or tetrahydrofuran), are highly effective in 1,4-additions to ot,P-enones (>85%) while the aryl heterozincates are less efficient (<50%).106... 

Table 2 lists the results found for the Grignard reagents investigated. In diethyl ether solution, the Grignard reagents preferentially add to C-1 [2], whereas in tetrahydrofuran (THF) and other solvents C-4 addition dominates [3], It was also reported that the addition of complexing agents such as iV,iV,iV, /V -tetramethylethylenediamine (TMEDA) or hexa-methylphosphoramide (HMPA) in diethyl ether resulted in the reversal of selectivity. 

The action of buQ Uithium on thioanisole in THF generates (phenylthio)methyllithium in a low yield of 35%. - Corey and Seebach found that reaction of equimolar amounts of bu Uithium, DABCO and thioanisole in THF at 0 "C produces (phenylthio)methyllithium in ca. 97% yield. Dimethyl sulfide can be metalated with a butyllithium-TMEDA complex at room temperature (equation 1). Treatment of chloromethyl p-tolyl sulfide with magnesium produces the corresponding Grignard reagent a reaction temperature between 10 and 20 C is crucial for its efficient generation (equation 2). ... 

Sulfonyl chlorides are totally defunctionalized (with loss of SO2 also) during coupling with Grignard reagents. Alkenylmagnesium bromides and alkyl halides (bromides and iodides) are coupled in the presence of FeCls and TMEDA, whereas for the formation of ArMgBr and RX a complex derived from FeCls and 1 has been identified. ... 

Preparative Methods coupling of the Grignard reagent derived from ( )-2-(trimethylsilyl)-l-bromoethylene with the same bromo derivative leads to the silyldiene in 51% yield a higher yield (62%) is obtained by reaction of bis(trimethylsilyl)-methyllithium with ( )-3-(trimethylsilyl)-2-propenal. Other procedures involve the Pd°-catalyzed demercuration of bis[( )-(2-trimethylsilylvinyl)]mercury, prepared from (i )-2-(tri-methylsilyl)-l-lithioethylene and HgCE (77% yield)7 or the reaction of ( j-l,4-bis(trimethylsilyl)-2-butene with n-BuLi and TMEDA and subsequent oxidation with HgCl2 of the isolated bis-lithiated species, stabilized by complexation with TMEDA (57% yield). ... 

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