Benzylic functionalization tertiary

The proposed mechanism is depicted in Scheme 38. The aldehyde is activated due to coordination on the silicon atom. A hydrogen bond between the aldehyde function and the benzyl substituted tertiary nitrogen atom stabilizes the transition state, and the benzyl group ensures that the cyclopentadiene attacks the dienophile only from one side. 

Some unusual benzylic functional groups can be reduced to hydrocarbons using NaBH4 alone in alcohols (equation 54). Choice of solvent can be used to enhance (or reduce) the reductive power of NaBIL. Thus in DMSO (or sulfolane), NaBH4 effectively reduces primary, secondary and tertiary benzylic halides to alkanes, leaving nitro, ester and carboxylic acids untouched (equation 55). There... 

Coupling reactions. Highly functionalized tertiary benzylic bromides are reduc-tively coupled by (PhyPfyCoCl. 

Selective ortho and benzylic functionalization of secondary and tertiary p-tolylsulfonamides is investigated (eq 47). For both R = H and R = Et, kinetic ortho metalation is achieved using BuLi, while thermodynamic conditions lead to ortho and benzylic deprotonation, respectively. Regioselective metalation of secondary sulfonamides, R = H, is achieved by using BuLi/KOtBu superbase. ... 

It is possible to effect reduction of tertiary benzylic hydroxy functions in the presence of primary halogens. Treatment of 1,1-diphenyl-l-hydroxy-2-haloethanes in chloroform with a slight excess of triethylsilane and a 9- to 10-fold excess of trifluoroacetic acid yields the corresponding 2,2-diphenyl-1-haloethanes (Eq. 45). The yield of the chloride is 77% after one hour at —15°, whereas that of the bromide is 66% following one hour at 0°.184... 

This tertiary amide-functionalized Schiff base thiourea was found to efficiently catalyze the asymmetric Strecker reaction [157] of N-benzyl-protected aldimines and also one ketimine in high enantioselectivities (86-99% ee) and proved superior to 42 examined under the same conditions (1 mol% loading, toluene, -78 °C, HCN) (Scheme 6.46) [198]. 

Figure 6.16 Structure optimization of 42 in the asymmetric Strecker reaction of N-benzyl-protected 2-methylpropionaldehyde imine identified tertiary amide-functionalized Schiff base thiourea 47 as the most enantioselective catalyst stmcture.

Previous discussions (20, 39) on the propagation rate, kp, point out the effect caused by the resonance energy of the radical formed. Our results support this view and enable us to complete the arrangement by families according to the groups adjacent to the attacked function—alkyl, benzyl, alkoxy, allyl, hydroxyl. The steric effect does not reveal itself in any important way—e.g., a-methylbenzylic ether has a kp which is close to that of benzylic ether, and the tertiary carbons in the former product are generally attacked at rates comparable with that of a less-encumbered carbon. 

The electrophilic amination reaction of organometallic species using mono-, di- and trihaloamines has attracted a lot of attention for the synthesis of amines. Only a few cases have been reported using alkylchloroamines as precursors for the synthesis of tertiary amines One example is the reaction of functionalized aryhnagnesium compounds with benzyl-V-chloroamines 252 providing polyfunctional tertiary amines 253 (equation 164) °. The procedure was also applied for the preparation of chiral V-chloro-amines with retention of chirahty at the a-carbon. However, the amination process is limited to benzyl-V-chloroamines. 

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