Dibenzyl ketone enolate

Dibenzyl ketone enolizes slightly to form a small amount of enol. 

The enolate of dibenzyl ketone adds to methyl vinyl ketone in the conjugate addition step. 

The first reaction is a mixed aldol condensation between the enolate of dibenzyl ketone and one of the carbonyl groups of the dione. 

An uncharacteristic enolate coordination is observed for the a,a -ketodianion derived fiom dibenzyl ketone (158).Hie dianion crystallizes as a bis-TMEDA solvate with the general structure shown as (159). Hie two lithium atoms are on opposite sides of the relatively planar carbon skeleton. Each is solvated by TMEDA. Besides coordination to the oxygen, the lithium atoms are in close contact with four additional carbon atoms. 

Dibromobenzene (55) is a good building block for cyclic compounds. The indanone 56 was obtained as expected by diarylation of dibenzyl ketone (14). On the other hand, a-arylation of benzyl tolyl ketone (57) with 55 afforded 58, and subsequent 0-arylation of the enolate 59 gave the furan 60 [40]. 

On the basis of Betti s initial work, the Betti reaction has been extended to both primary amines and secondary amines. The resulting Betti amines have been applied as ligands or chiral auxiliaries in asymmetric synthesis. In addition, the Betti reaction has also been extended to the reaction among aldehydes, secondary amines, and compounds of active methylene moiety, such as dibenzyl ketones which can tautomerize to enols and mimic naphthol. Moreover, the reaction of aromatic aldoximes and 0-keto esters to afford isoxazolones should also be considered as an extension of the Betti reaction. 

Monomeric lithium enolates were rarely characterized by crystal structure analysis. It seems that prerequisite to monomer formation is an optimal solvation of the counterion lithium only if the metal is satisfied by a threefold, strong coordination by an external cosolvent, a monomeric enolate was detectable in the crystal state. This is illustrated by a crystal structure of the lithium enolate of dibenzyl ketone grown from a THF/diethyl ether solution containing the tri-dentate amine ligand A/ M M M" M"-pentamethyldiethylenetriamine (PMDTA), shown in Figure 3.4 [16a]. 

Figure 3.4 Structure of the monomeric lithium enolate of dibenzyl ketone with the metal complexed by the tridentate PMDTA ligand. Copied from Ref. [16a].

This finding is also in agreement with another three-component Michael/aldol addition reaction reported by Shibasaki and coworkers [14]. Here, as a catalyst the chiral AlLibis[(S)-binaphthoxide] complex (ALB) (2-37) was used. Such hetero-bimetallic compounds show both Bronsted basicity and Lewis acidity, and can catalyze aldol [15] and Michael/aldol [14, 16] processes. Reaction of cyclopentenone 2-29b, aldehyde 2-35, and dibenzyl methylmalonate (2-36) at r.t. in the presence of 5 mol% of 2-37 led to 3-hydroxy ketones 2-38 as a mixture of diastereomers in 84% yield. Transformation of 2-38 by a mesylation/elimination sequence afforded 2-39 with 92 % ee recrystallization gave enantiopure 2-39, which was used in the synthesis of ll-deoxy-PGFla (2-40) (Scheme 2.8). The transition states 2-41 and 2-42 illustrate the stereochemical result (Scheme 2.9). The coordination of the enone to the aluminum not only results in its activation, but also fixes its position for the Michael addition, as demonstrated in TS-2-41. It is of importance that the following aldol reaction of 2-42 is faster than a protonation of the enolate moiety. 

As depicted in Scheme 1.1.2, the silyl ketones (S)-ll of high enantiomeric purity were converted into the Z-configured silyl enol ethers (S) -12, which were used in the aminomethylation step by treatment with dibenzyl(methoxymethyl)amine in the presence of a Lewis acid. The silylated Mannich bases S,R)-13 were obtained in excellent yields and diastereomeric excesses (de = 92-96%). Finally,... 

S )-Dibenzyl l-(l-Oxo-l,2,3,4-tetrahydronaphthalen-2-yl)hydrazine-l,2-dicarboxylate (Catalyzed Asymmetric Amination of a Ketone Silyl Enol Ether with an Azo Ester).244 A solution of silver perchlorate (0.040 mmol) and (R)-BINAP (0.048 mmol, 12 mol%) in THF (1 mL) was stirred at room temperature for 30 minutes, cooled to —45°, and treated with dibenzyl azodicarboxylate (0.44 mmol). After stirring for 10 minutes, (3,4-dihydronaphthalen-l-yloxy)trimethylsilane (0.4 mmol) in THF (0.5 mL) was added and the mixture was stirred at —45° for 5 hours. Aqueous HF (20%) and THF (1 1) were added and the mixture was stirred at room temperature for one hour after which time it was made basic with aqueous NaHCC>3 solution and extracted with CH2CI2. 

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