Reductive lithiation chlorides

If further acidic C—H bonds in the molecule cause problems, the tin-trick can be applied. The asymmetric deprotonation of a bifunctional carbamate (39a) is accomplished at an early stage and the masked carbanionic centre carried through the synthesis as a stan-nyl group. For instance, the (S)-5-silyloxy-l-tributylstannyl-pentyl carbamate 39b (> 95% ee) was produced by the usual means and converted by standard steps via the aldehyde 78 into the allyl chloride 79 (equation 17) . Lithiodestannylation of 79 by n-BuLi proceeds faster than reductive lithiation in the allylic position to form the lithiocarbamate 80,... 

Fig. 17.46. Reductive lithiation of an alkyl aryl sulfide (Screttas-Cohen process) and an alkyl chloride (Screttas-Yus process).

Fig. 17.47. Reductive lithiation of a carbamoyl chloride to the (dialkylamino)carbonyl lithium compound A and its immediately following reaction with a carbonyl compound (Barbier reaction) leading to alcohol B.

Similar reductive lithiations are available from 2-deoxy sugars. As shown in Scheme 3.2.3, tri-O-benzyl glucal was converted to the desired 2-deoxy glucopyranosyl chloride on treatment with hydrochloric acid. Following formation of the chloride, Lancelin, etal.,14 effected formation of the a lithiated sugar, via initial conversion to the axially oriented anionic radical, on treatment with lithium naphthalide. 

Complimentary to the use of pyranosyl chlorides as substrates for reductive lithiations is the use of pyranosyl phenylsulfones. These species are... 

Aqueous titanium (III) chloride reductively removes cyano and halo groups from substituted pyridines by a two-electron process and promotes reduction of pyridyl ketones and aldehydes to glycols by a one-electron-transfer process.49 a useful review of the reactions of halopyridines with lithiating reagents is now available.50 Choice of reaction conditions can be critical thus, depending on the conditions, 3-fluoropyridine can be converted into either 2- or 4-lithio-3-fluoropyridine and therefore be used as a precursor of both 2,3- and 3,4- disubstituted pyridines. 

Preparative Methods lithiation of 1,3-dichloropropene followed by treatment with a silyl chloride reaction of 1,3-dichloropropene with Mg° and a silyl chloride electrophile treatment of allylsilanes with BuLi/TMEDA and a silyl electrophile reaction of allyl alcohol with HMPA, Mg°, and a Lewis acid catalyst cross-metathesis of allylsilanes reductive lithiation of allylthioethers. ... 

Functionalized heterocyclic zinc reagents are quite usefiil for the preparation of polyfunctional heterocycles. The pyridylzinc derivative 400 has been prepared by reductive lithiation followed by a transmetalation with zinc bromide (Scheme 2-130, eq. (a)). Its cross-coupling with a quinolyl chloride provides the new polyheterocyclic compound 401 in 81% yield. The selective functionalization of positions 3 and 4 of... 

The preparation of 1 started with the addition of lithiated 4 to the enantiomcrically-pure epoxide 5, which was prepared from the racemate using the Jacobsen protocol. Reduction followed by selective protection of the primary alcohol gave the monosilyl ether, which was further protected with MOM chloride to give 7. Pd-mediated oxidation to the methyl ketone followed by condensation with the Horner-Emmons reagent gave the unsaturated ester 8 as an inconsequential mixture of geometric isomers. Oxidation then set the stage for the crucial cyclization. 

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