Stoichiometric additive

A method for the stoichiometric addition of metallo-aldehyde enolates to ketones has recently been reported K. Yachi, H. Shinokubo, K. Oshima, /. Am. Chem. 

Alcoholysis of meso-cycYic anhydrides offers a versatile route to succinate and glu-tarate half-esters. Although a number of stoichiometric approaches to this problem have been investigated, a successful catalytic version of this reaction appeared as recently as 2003. ° Bolm and coworkers have developed a protocol for the metha-nolysis of a variety of succinic anhydrides using cinchona alkaloids [Eq. (10.50)]. The reaction may be made catalytic in alkaloid when pentamethylpiperidine is used as a stoichiometric additive. A moderate decrease in enantioselectivity is observed in a number of cases, although excellent selectivities are still attainable. More problematic is the reaction time (6 days under catalytic conditions) ... 

More recent reports from Cordova [155] and Wang [156] have described the cyclopropanation of a, P-unsaturated aldehydes 99 with diethyl bromomalonates 100 and 2-bromo ethyl acetoacetate catalysed by a series of diaryIprolinol derivatives. Both describe 30 as being the most efficient catalyst in many cases and optimal reaction conditions are similar. Some representative examples of this cyclopropanation are shown in Scheme 40. The transformation results in the formation of two new C-C bonds, a new quaternary carbon centre and a densely functionalised product ripe for further synthetic manipulation. Triethylamine or 2,6-lutidine are required as a stoichiometric additive in order to remove the HBr produced during the reaction sequence. The use of sodium acetate (4.0 equivalents) as an additive led to subsequent stereoselective ring opening of the cyclopropane to give a,P-unsaturated aldehydes 101. It can be envisioned that these highly functionalised materials may prove useful substrates in a variety of imin-ium ion or metal catalysed transformations. 

The catalyst is generally a palladium compound promoted with a trivalent amine or phosphine in the presence of methyl iodide as described earlier. Systems proven to bias acetaldehyde are utilized, of course (e.g. see Table I, run 12). A yield of 85% acetaldehyde from methyl acetate is typical by this method. It can be utilized in stoichiometric addition to easily prepared acetic anhydride resulting in EDA formation. When considering that the "boiling pot" reaction by-products are recyclable acetic acid, acetic anhydride and small amounts of EDA, the yield to vinyl acetate related products is 95%. 

The formation of chiral alcohols from carbonyl compounds has been fairly widely studied by reactions of aldehydes or ketones with organometallic reagents in the presence of chiral ligands. Mukaiyama et al. 1081 obtained excellent results (up to 94% e.e.) in at least stoichiometric addition of the chiral auxiliary to the carbonyl substrate and the organometallic reagent. 

V,A,iV, Ai -Tetraethyl-l,l -bi-2-naphthol-3,3 -dicarboxamide (20) has been shown by KatsuTi and coworkers to be quite effective as a stoichiometric additive in the cyclopropanation of allylic alcohols (equation 89) . The best enantioselectivities were obtained with aryl-substituted allylic alcohols however, 6 equivalents of diethylzme were needed. 

Cu and Zn can entirely be removed from BESOD by chromatography on a Sephadex G-25 column by elution with 10 mM EDTA at pH 3.8 At this pH the apoprotein is stable and a total reconstitution was achieved by the stoichiometric addition of Cu and subsequently of Zn, followed by a dialysis against phosphate buffer pH 7.8. Zn could also be replaced by Co, Cd, and Hg yielding active products. The (Cu,—)-derivative with an empty Zn site was only partially active . It is important in such experiments to remove EDTA entirely from the apoprotein, like by a dialysis against 0.1 M NaClO ... 

EvO. — This lower oxide of europium was prepared by the reduction of EuaOs with lanthanum metal at 1300 —1500° C by Eick et al. [319]. EuO has a NaCl type structure with a = 5.1439 0.0005 A. Gaston and Hukln [320] attempted the preparation of EuO by controlled oxidation of europium metal at 350° C with a stoichiometric addition of oxygen and obtained the oxide in fairly pure state. They also tried the thermal decomposition of EuCOs, Eu(HCOO)2 and Eu(OH)2. Only Eu(OH)2 proved to be advantegeous and gave a sample of EuO of reasonable purity. 

Bismuth(III) oxide, Bi O is the compound produced by heating the metal, or its carbonate, in air. It is definitely a basic oxide, dissolving readily 111 acid solutions, and unlike the arsenic or antimony compounds, not amphiprotic in solution, although it forms stoichiometric addition compounds on heating with oxides of a number of other metals. It exists in three modifications, white rhombohedral, yellow rhombohedral, and gray-black cubical, Bismuth(II) oxide. BiO, has been produced by heating die basic oxalate. 

In the first step the free hydroxy group is protected as a ten-butyl dimethyl si lyl ether Then the lactone is reduced to a lactol, which is the cyclic herniacetal of an aldehyde. Overreduction to an alcohol can be prevented by stoichiometric addition of the reducing reagent at low temperature. Selectivity here depends on the relative stability of intermediate 19, which decomposes only in the course of workups (see Chapter 3). 

Conjugate additions of carbamates to a, P-unsaturated enones require - apart from metal halide - TMSC1 as a stoichiometric additive [96]. The addition of ethyl carbamate to cyclohexenone (41h) requires only 50mol% TMSC1, which was an exceptionally low amount compared with other Michael acceptors. With 10 mol% of the catalyst, the yield of 3-aminocyclohexenone derivative 66 was good (93%) [97], Aza-Michael reactions also proceed in aqueous media with good results if Co(II),... 

Finally stoichiometric addition of DIBAH in a nonpolar solvent at low temperature yields the desired aldehyde 11. Overreduction to the corresponding alcohol 33 is prevented under these conditions because of the formation of the relative stable intermediate 34, which decomposes only in the course of aqueous work-up. At higher temperature and in polar solvents such as THF formation of alcohol 33 occurs. Thus, grade of reduction of esters with DIBAH can be controlled by temperature and solvent. 

A solution of living PI chains was added to a large excess of the silane, followed, after the evaporation of the excess trichloromethylsilane, by the slow stoichiometric addition (titration) of the living PS chains, exactly as was described in the case of the A2B2 star copolymers. The formation of the desired product, (PS)(PI)(CH3)SiCl was monitored by SEC taking samples from the reactor during the titration process. The ABC star was finally prepared by the addition of a slight excess of PBLi. 

An eliminative mechanism denoted ERC1, has been shown to occur in conjunction with the SRN1 mechanism in certain systems (Norris and Smyth-King, 1979 and references cited therein). It is, however, of a type different in principle from SRN1, being a reductive elimination (see Table 2) which requires a stoichiometric addition of electrons. 

The oxidation of bromide can be conveniently and quantitatively measured by the bromination of TMB in DMF solution. Bromination is stoichiometric with the vanadium complex concentration in the absence of added acid (35). The stoichiometric addition of acid results in an... 

We speculated earlier whether a fluoride ligand could add catalytic properties to our chiral dialkoxy cyclopentadienyltitanium complexes. Chlorotitanium-TADDOLate 17 - an excellent template for controlling the stereochemistry of stoichiometric additions also to chiral aldehydes... 

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