Nucleophilic addition reactions reagents

In most cases of diastereoselective nucleophilic addition reactions where achiral organometallic reagents are added to chiral carbonyl compounds, the chirulity inducing asymmetric center is in close vicinity to the newly created center and cannot be removed without the loss of chirality of either the inducing center or the newly formed center. This type of reaction is very useful in propagating chirality in a molecule from one center to an adjacent one, or in immolative processes. 

Nucleophilic addition reactions of allylic tin reagents to chiral 3-substituted 3,4-dihydroisoquinolines 89 activated by acyl chlorides afford trans 1,3-disubstituted 1,2,3,4-tetrahydroisoquinolines 90 stereoselectively <95CL1003>. 

Nitrones have a more reactive C=N bond toward nucleophilic addition compared to imines. In spite of this fact, there have been only a limited number of studies on the nucleophilic addition reactions of nitrones, particularly organometallic reagents.352-355 During the last decade, research related to reactions of nitrones with zinc-containing reagents was essentially focused on (i) dialkylzinc-assisted alkynylations356-358 and vinylations359 of nitrones, (ii) catalytic asymmetric nucleophilic additions to the C=N bond,360-364 and (iii) nitrone allylations by allylzinc halides.365,366... 

Reactions of highly electron-rich organometalate salts (organocuprates, orga-noborates, Grignard reagents, etc.) and metal hydrides (trialkyltin hydride, triethylsilane, borohydrides, etc.) with cyano-substituted olefins, enones, ketones, carbocations, pyridinium cations, etc. are conventionally formulated as nucleophilic addition reactions. We illustrate the utility of donor/acceptor association and electron-transfer below. 

Subsequently, Corey and coworkers40 42 described nucleophilic addition reactions of organocopper reagents and organocuprates to several acceptor-substituted dienes. The... 

The formation of this product need not concern us, hut its nature is important, in that it contains the equivalent of R or Ar , i.e. the alkyl or aryl group has been transformed into its carbanion. Addition of an aldehyde or ketone to the solution of the Grignard reagent allows a nucleophilic addition reaction to occur. The reaction resembles that of... 

Nucleophilic addition reactions to oxathiazinane N,0-acetals proceed smoothly with al-lylsilane, alkynylzinc, silyl enol ether, and silylketene acetal reagents (Scheme 17.22)... 

When a stepwise ionic addition reaction involves nucleophilic attack at carbon as a first step, it is described as a nucleophilic addition. Reactions of this type often are catalyzed by bases, which generate the required nucleophile. For example, consider the addition of some weakly acidic reagent HX to an alkene. In the presence of a strong base ( OH), HX could give up its proton to form the conjugate base Xe, which is expected to be a much better nucleophile than HX ... 

An alternative stereoselective synthesis of chiral heterocycles based on carbohydrate-induced stereodifferentiation includes nucleophilic addition reactions on heterocyclic systems already bound to the carbohydrate auxiliary. An example of this strategy has been shown by stereoselective addition of Grignard reagents to carbohydrate-linked 4-pyridones [61]. For this purpose, trimethylsiloxypyridine was glycosylated regioselectively using pivaloyl-protected glycosyl fluorides. 

The high 77-deficiency at C-7 is also apparent from the nucleophilic addition reaction with sodium borohydride selective formation of the 6,7-dihydro derivative (566) results with this reagent. The reaction may also proceed further by reductive loss of the 7-substitutent (76CPB235). In the pyrazine analogue (567) both LAH and sodium borohydride treatment lead to saturation of the pyrazine ring (78JOC341). 

---