Benzoin formate ester

In an attempt to use an acyl anion equivalent to open an aziridine, Wu and co-workers isolated an unexpected ring opened product 316 (Eq. 31) [158], The authors found that the presence of oxygen was the determining factor between benzoin formation and ester formation. No desired ketones were ever formed. Various aromatic substituted aldehydes were treated under standard reaction conditions to afford esters in good yields. 4-Methoxybenzaldehyde provided product in only 40% yield, presumably due to the ease of aldehyde oxidation. 

Quinoxaline-2-carboxaldehyde has been converted into the 2-carboxylic acid by oxidation with potassium permanganate in acetone and reduced to the 2-hydroxymethyl compound by treatment with formalin and potassium hydroxide. It also undergoes other typical reactions of aromatic aldehydes such as benzoin formation on reaction with potassium cyanide - and condensation reactions with malonic acid and its diethyl ester and Schiff base formation. Acid-catalyzed reaction of quinoxaline-2-carboxaldehyde with ethylene glycol gives the cyclic acetal the diethylacetal has been prepared by reaction of 2-dibromomethylquinoxaline with sodium ethoxide. " An indirect preparation of the oxime 11 is achieved by treatment of 2-nitromethyl-quinoxaline (10) with diazomethane followed by thermolysis of the resulting nitronic ester. 

A reaction pathway involving a concerted transition state of the type (210) has been shown to be compatible with the kinetic results and formation of 1,2-diarylethanones observed during the gas-phase pyrolysis of the formate ester of benzoin and the... 

Regio-control of the formation of benzoic esters of mixed benzoin derivatives results from the initial formation of the cyanhydrin benzoate (see Chapter 3). Subsequent base-catalysed hydrolysis of the esters produces the mixed benzoins (Scheme 6.20) [66]. 

Bode and co-workers further extended redox esterification to include carbon-carbon bond breaking of formyl-cyclopropanes [113]. Both esters and thioesters are formed in high yield and good enantioselectivities (Scheme 31). The M-mesityl substituted triazolium salt 191 proved to be the most efficient pre-catalyst providing complete suppression of the benzoin reaction. Electron-deficient substituents, such as phenyl ketone, readily provide ester formation. 

The apparent fickleness of the acyl-pyrroles and -indoles in their reaction with carbanions to form new C—C bonds arises from the contribution made by the zwitterionic structure, e.g. (410b), to the resonance hybrid and the choice of the reaction conditions is critical for a successful nucleophilic reaction. Thus, formyl-pyrroles and -indoles do not normally undergo the Cannizzaro reaction nor do they form stable cyanohydrins or undergo benzoin-type reactions. However, surprisingly, 2-formylpyrrole reacts with arylaldehydes in the presence of potassium cyanide to yield (428), which is easily oxidized to (429) (B-77MI30505). It is noteworthy that the presence of an ester substituent adjacent to the formyl group modifies the mesomeric interaction to such an extent to allow the formation of (430) in low yield, as a result of an initial benzoin-type self-condensation (Scheme 76) (68BSF637). 

Peach et al. developed a general, racemization free, and high yield procedure for the synthesis of O-desyl peptide esters from the poorly nucleophilic benzoin.1261 Employing the cesium salt of the model dipeptide Z-Gly-Phe-OH in acetone the intramolecular hydantoin formation obtained in polar aprotic solvents, such as DMF and DMSO, can be suppressed and a high yield of Z-Gly-Phe-O-desyl with ee >90% can be generated. 261 ... 

Capillaries packed with poly-A-acryloyl-L-phenylalanine ethyl ester (Chiraspher) modified silica were used for electrochromatographic enantiomer separation of ben-droflumethiazide. To suppress bubble formation, the inlet buffer vial was pressurized to 12 bar and the outlet buffer vial to 4 bar [42], Acetonitrile or methanol were used as organic modifier whereby acetonitrile was superior to methanol. Non-aqueous p-CEC was performed on helical poly(diphenyl-2-pyridylmethylmethacrylate) coated on wide-pore aminopropyl silica [56]. With this chiral stationary phase, the enantiomer separation of Trogers base, benzoin acetate, methylbenzoin and trans-stilbene oxide was achieved by pressure-supported CEC, applying a higher pressure to the inlet than to the outlet buffer vial. 

C—C—O—C+N. The formation of oxazoles from a-acyloxy ketones and ammonium salts was discovered in 1937 when it was found that treatment of benzoin benzoate with ammonium acetate in hot acetic acid gave triphenyloxazole in excellent yield. It has been shown that the reaction proceeds by way of intermediate enamines (equation 113). The synthesis is quite general and it is only.limited by the difficulty of obtaining the starting keto esters, particularly formates. The latter are probably intermediates in the preparation of cycloalkenooxazoles from acyloins and formamide in hot sulfuric acid (equation 114). Another variation is to heat a mixture of an a-bromo ketone, the sodium salt of a carboxylic acid and ammonium acetate in acetic acid (equation 115). 

Sulfonic (-SO3H) and Sulfinic (-SO2H) Acid-Based Nonsalt Photoinitiators Photosensitive tosylate esters of nitrobenzyl [65] and benzoin [73], sulfonyl ketones [67,68], and diphenyl disulfones [68] can be employed in cationic photopolymerization, especially in photolithography and chemical amplification processes. The advantages of these photoinitiators are the ease of synthesis, the absorption wavelengths suitable for deep-UV curing and the high yield of acid formation [65]. 

It is prepared by the eondensation of two moleeules of benzaldehyde with sodium cyanide to get benzoin, which on treatment with nitric acid or cupric sulphate forms benzil. In the presence of sodium ethoxide, benzil in hot condition yields benzilic acid ester, (a) The latter on condensation with urea in the presence of sodium ethoxide give rise to phenytoin the enol-form of which on neutralization with sodium hydroxide ultimately results into the formation of phenytoin sodium. 

Acyloin condensation. The usual preparation of acyloins from aliphatic esters is not applicable to aromatic esters. In this case the reaction with sodium results in formation of the sodium carboxylate and a radical from the R group which undergoes further reactions. However, benzoin can be prepared in moderate yield by treatment of the trimethylsilyl ester of benzoic acid with sodium or by treatment of ethyl benzoate with sodium naphthalenide in THF at room temperature (397 yield). ... 

This reaction was first reported by Bouveault and Blanc in 1903, and was further extended by Bouveault and Locquin. It is the synthesis of symmetrical a-hydroxy ketones via the reductive condensation of esters in an inert solvent in the presence of sodium. Since symmetrical a-hydroxy ketones, the aliphatic analogs of benzoins, are generally known as acyloins, the formation of a-hydroxy ketones from esters is simply referred to as acyloin condensation. In a few cases, it is also referred to as acyloin reaction." For the individual acyloin, the name is derived by adding the suffix oin to the stem name of corresponding acid, e.g., acetoin prepared from acetate. The most common method used to make acyloin is the reductive condensation of aliphatic esters with sodium in inert solvents, such as ether, xylene or even in liquid NH3 The yield of this reaction can be greatly improved when trimethylchlorosilane presents." " Intromolecular acyloin condensation from aliphatic diesters affords cyclic ketones of different ring sizes. 

Aromatic aldehydes, Ar CHO, have been cross coupled with diarylbromomethanes, Ar Ar CHBr, to give diaryl acetophenone derivatives, Ar COCHAr Ar, using NHC catalysis. A benzoin can be used as a masked aldehyde in the reaction, indicating that the formation of the Breslow intermediate is reversible. The utility of the reaction has been extended on the halide side a-halo ketones and esters can serve in place of diarylmethyl bromides. 

In an acetonitrile suspension, the intermediate a-cyanoalkoxide can be trapped by acyl chlorides to give cyanohydrin esters. In a preparation of synthetic pyrethroids, the comparison between the sonicated reaction and its PTC equivalent gave an advantage to the latter in terms of reaction time and yield. i A modest change in stereoselectivity is observed in some cases. The same reaction in the presence of ammonium chloride leads to a-amino nitriles, the first step of the Strecker amino acid synthesis.4 72 xhe procedure is more efficient in the presence of alumina. The formation of by-products, cyanohydrins or benzoins, is avoided. From an experimental viewpoint, the work-up is considerably easier than with conventional procedures, and consists mostly of a simple filtration. With ketones, and in the presence of ammonium carbonate, a hydantoin is formed (Eq. 21)7 ... 

Furans and Benzofurans.—Formation. The acid-catalysed condensation of 2-chlorocyclopentanone with dimethyl jS-oxoglutarate leads to the furan ester (100). Compound (101) is obtained by the action of nitrotrichloroethylene on acetylacetone in the presence of bases. 1-Diethylaminopropyne, MeC=CNEt2, and benzoin undergo three competing reactions to give a mixture of the furans (102) and (103) and the butenolide (104). The sulphonium ylide (105) and... 

Alternatively, the oxidation may occur by coupling to a suitable reactant. In 1997, Miyashita explored the scope of oxidative aroylations with nitrobenzene (Scheme ll.lO)." With the same oxidative reagent, nitrobenzene, benzoin reactions had already been developed back in 1982 using cyanide or thiamine. The combination of an aldehyde and nitrosobenzene, in the presence of an NHC, led to the formation of 7V-phenyl hydroxamic acids in good yields. These can be further converted into hydroxamic esters via a one pot reaction in the presence of a second (o,p-unsaturated) aldehyde. Furthermore, the oxidative coupling of aldehydes with carbodiimides in air allowed access to Af-acyl urea derivatives with IMes HCl 19 as the NHC precursor. Related thioesterifications reactions have also been reported using... 

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