Deprotonative metalation pairs

Deprotonation of 3-methoxy-3-methylallene with BuLi followed by metal exchange with Ti(OiPr)4 affords a chiral allenyltitanium reagent [31], Addition of this reagent to enantioenriched (S)-2-benzyloxypropanal afforded a mixture of four diastereomeric products in which the anti,syn and anti,anti adducts predominated (Eq. 9.26) [31], The former was shown to derive from the matched pairing of the (S)-aldehyde with the (P)-enantiomer of the allenic titanium reagent. The latter is the major diastereomer of the mismatched (S)/(M) pairing. 

Conversion of tight ion pairs into crown ether-separated ion pairs leads in many cases to increased basicity. For example, Dietrich and Lehn (1973) have shown that a homogeneous solution of sodium t-amyloxide in benzene is unable to deprotonate triphenylmethane, whereas the reaction occurs rapidly in the presence of [2.2.2]-cryptand [37]. In THF or diethyl ether, alkali metal enolates do not react with triphenyl- or diphenylmethane (Pierre et al.,... 

A remarkable aspect of the heterobimetal lie magnesium salts is the discovery that compounds, derived from the pairing of two different metal atoms usually Li, Na, or K and Mg or Zn that are bound by amido ligands, can deprotonate arene rings [(tmeda)Na-... 

Figure 12.8.2(a) shows the molecular structure of Na4Mg2(TMP)6(C6H4), in which the N atom of each tetramethylpiperidinide is bonded to two metal atoms to form a cationic 12-membered (Na-N-Na-N-Mg-N-h ring. The mixed metal macrocyclic amide acts as a host that completely encloses a 1,4-deprotonated benzenediide guest species whose naked carbon atoms are each stabilized by a covalent Mg-C bond and a pair of Na- C n interactions. 

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