Lithium reagents configurationally stable

The chiral silyllithium reagent methyl(naphthyl)(phenyl)silyl-lithium is configurationally stable at and below room temperature, and reacts with methyl(naphthyl)(phenyl)silyl chloride with retention at the nucleophilic silyl group and inversion at the electrophilic silyl group... 

Still, W. C. Sreekumar, C. a-Alkoxyorgano-lithium reagents. A new dass of configurationally stable carbanions for organic synthesis./. Am. Chem. Soc. 1980, 102, 1201—1202. 

The homolytic cleavage of the carbon-sulfur bond generates an intermediate radical 17 that adopts an axial orientation. The second electron transfer gives a kinetic a-oriented and configurationally stable lithium reagent 18, which is protonated with retention of configuration. Again, the transient radical defines the stereochemical outcome of the overall process. 

Reactions of Boc BMI with Electrophiles. The enolate of Boc-BMI is generated with Lithium Diisopropylamide in THF at -75 °C the resulting solutions of this highly nucleophilic reagent are stable up to 0 °C. All reactions occur from the face of the enolate trans to the t-Bu group at C(2). Alkylations even with secondary alkyl halides are so efficient, to give (3), that one-pot double alkylations, which yield (4), are possible the sequence in which two different alkyl halides are employed determines the absolute configuration of the ot-branched ot-amino acids eventually obtained. 

The deprotonations are complete within a few hours at -78 °C and afford the lithium car-benoid sparteine complexes (5)-l-(-)-3 with excellent enantioselectivities. [6-12] Whereas sparteine complexes of lithiated secondary allyl and primary alkyl carbamates are configurationally stable below -30 °C, those of primary allyl carbamates such as 4 (-)-3 are not configurationally stable even at -70 °C. It is, however, possible to use these reagents in synthesis, since the preferential crystallization of the S diastereomer in pentane/cyclohexane drives the equilibrium completely to one side. After a low-temperature transmetalation of (5 )-4-(-)-3 with an excess of tetraisopropo-xytitanium, the allylic titanium reagent (Ji)-S is obtained with inversion of configuration. The addition of various aldehydes to (R)-5 furnishes homoaldol adducts of type 6 with... 

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