Enolates and Related Derivatives

Negishi, E.-i. Palladium-catalyzed cross-coupling involving 3-hetero-substituted compounds. Palladium-catalyzed a-substitution reactions of enolates and related derivatives other than the Tsuji-Trost allylation reaction. Handbook of Organopalladium Chemistry for Organic Synthesis 2002, 1, 693-719. 

III.2.14.1 Palladium-Catalyzed of-Substitution Reactions of Enolates and Related Derivatives Other than the Tsuji-Trost Allylation Reaction... 

In this section, attention is focused on the Pd-catalyzed a-substitution reactions of enolates and related derivatives represented by Method I in Scheme 1, other than Tsuji-Trost allylation and propargylation. Additionally, its charge-affinity inverted version represented by Method II in Scheme 1 is also discussed. In general, it is advisable to consider simultaneously various other alternatives including those shown in Scheme 1, especially Method III. Indeed, Method III discussed in the following section provides the currently most... 

Esters, Nitriles, Amides, Mines, and Enamines. Pd-Catalyzed a-arylation of extrastabilized enolates and related derivatives containing esters and nitrile groups developed by Uno, Takahashi, and co-workersf (Sect. B.i.b,) has been applied to the synthesis of cyclic compounds with moderate success, as indicated by the results shown in Scheme... 

Pd-Catalyzed Acylation, Cyanation, and a-Substitution of Enolates and Related Derivatives... 

V.2.1.4 Palladium-Catalyzed Allylation and Related Substitution Reactions of Enolates and Related Derivatives of Ordinary Ketones, Aldehydes, and Other Carbonyl Compounds... 

B. SCOPE, LIMITATIONS, MECHANISM, AND APPLICATIONS OF THE PALLADIUM-CATALYZED a-ALLYLATION OF METAL ENOLATES AND RELATED DERIVATIVES... 

Negishi E, Makabe H (2002) Reactions of Acylpalladium Derivatives with Enolates and Related Amphiphilic Reagents. In Negishi E, de Meijere A (eds) Handbook of Organopalladium Chemistry for Organic Synthesis. Wiley, New York, p 2455... 

Samarium has two common oxidation states +2 and -h3. Upon solution in toluene under nitrogen, an anionic Sm(II) species, [(—CH2—)5]4-calix-tetrapyrrole Sm(THF)[Li (THF)]2[Li(THF)2]Cl, forms, in part, the compound [(—CH2—)5]4-calix-tetrapyrrole Sm(THF)Li2[Li(THF)](/r -OCH=CH2) . However, this compound is a lithium enolate derived by elimination of THF. In that the metalloorganic reagent is rather similar to what will be discussed in Section XI as part of vanadium enolate chemistry, we fail to understand why in the former case with Sm a lithium enolate is formed but in the latter with V it is an ynolate that is produced. Almost nothing is known to allow comparing the energetics of metal enolates and related ynolates. We note from the enthalpies of... 

Only a few cases of the reduction of alkyl enol ethers to the corresponding alkene have been reported. a-Ethoxystyrene and related derivatives are reduced to alkenes by treatment with Grignard reagents. In addition, enol ethers of cyclohexanone derivatives have been cleaved to the cyclohexene products using either DIBAL at elevated temperatures or diborane/boron trifluoride etherate. By analogy to the hy-droboration of silyl enol ethers, this latter method involves formation of an intermediate p-ethoxy or-ganoborane which undergoes acid-catalyzed elimination to afford the alkene. 

Finally, the C—C bond formation by the reaction of 7r-complexes of Pd derived from alkenes, dienes, and other 7r-compounds with enolates and related carbon nucleophiles a la Wacker reaction (Method VI in Scheme 1) provides yet another alternative, as exemplified by the results shown in Scheme For a more general discussion of the C—C bond formation via Wacker-type reaction of Pd rr-complexes with carbanions, the reader is referred to Sect. V.3.4. 

Jones and colleagues have prepared 1,4-dicarbonyl compounds by conjugate additions of enolate and related anions to a,P-unsaturated sulfoxides [80,81]. For example, the lithium enolate of acetone dimethylhydrazone (83), in the presence of dimethyl sulfide-copper(I) bromide complex, underwent conjugate addition to 2-phenylsulfinyloct-l-ene (82). Quenching the reaction mixture with dimethyl disulfide gave the doubly protected 1,4-diketone derivative (84), which, on sequential hydrolysis with copper(II) acetate and trifluoroacetic acid gave the dodecane-2,5-dione (85) as the product in 54% yield from (82) (Scheme 5.27). Other examples of the addition of enolate-type species to a,p-unsaturated sulfoxides have also been reported [82.83]. 

Cyclohexenones and Related Derivatives. House and Wilkins have now demonstrated that addition of lithium dimethylcuprate to 3-methylcyclohex-3-enone in 1 1 molar equivalents results in a solution of the lithium enolate and a precipitate of (MeCu). Even when soluble cuprous species occur, there is no evidence to suggest that reaction with lithium enolates to give copper(i) enolates occurs. In a 1,4-addition reaction phenylithio[(a-diethoxymethyl)vinyl] cuprate with cyclohexenone at 233 K in Et20 gave ultimately 88% of the 3-allylcyclohexanone (38) (a-diethoxymethyl)-vinylcopper gave the 1,2-addition product. 

Acyl enolate and related equivalents 10.2.1.1.4.1 Simpie acyi derivatives... 

VI.2.3 Reactions of Acylpalladium Derivatives with Enolates and Related Amphiphilic Reagents... 

Most of the reactions of ester enolates described so far have centered on stabilized eno lates derived from 1 3 dicarbonyl compounds such as diethyl malonate and ethyl ace toacetate Although the synthetic value of these and related stabilized enolates is clear chemists have long been interested m extending the usefulness of nonstabilized enolates derived from simple esters Consider the deprotonation of an ester as represented by the acid—base reaction... 

Aldol Addition and Related Reactions. Procedures that involve the formation and subsequent reaction of anions derived from active methylene compounds constitute a very important and synthetically useful class of organic reactions. Perhaps the most common are those reactions in which the anion, usually called an enolate, is formed by removal of a proton from the carbon atom alpha to the carbonyl group. Addition of this enolate to another carbonyl of an aldehyde or ketone, followed by protonation, constitutes aldol addition, for example... 

---